Add option for file count only

[cosad3s]

I needed something to only count files, classified by language. I like subroutines of cloc to identify languages but I was not satisfied by the performance drop caused by the line counting on big repositories (Which I do not need in my case). So I propose an option --only-count-files to skip line count.

Example on bash mirror repository https://github.com/bminor/bash :

❯ time ./cloc .
    1404 text files.
     587 unique files.                                          
     868 files ignored.

github.com/AlDanial/cloc v 1.97  T=0.73 s (801.4 files/s, 715967.8 lines/s)
---------------------------------------------------------------------------------------
Language                             files          blank        comment           code
---------------------------------------------------------------------------------------
PO File                                 39          25332          32315         170056
C                                      271          22627          21970         117193
HTML                                     3           4019             30          27309
Bourne Shell                            40           4513           3864          25686
Windows Module Definition               44           2676              9          15657
C/C++ Header                           113           2934           3591           8133
m4                                      40            663            829           7648
TeX                                      1            821           3462           6762
yacc                                     2            855            980           5411
Perl                                     2            535            834           4229
Text                                     4            363              0           1342
Bourne Again Shell                      16            177            327            769
Markdown                                 1             30              0            136
make                                     3             50             36            122
Assembly                                 2             11             20             48
awk                                      1              8             15             24
sed                                      2              0              0             16
TNSDL                                    3              0              0              5
---------------------------------------------------------------------------------------
SUM:                                   587          65614          68282         390546
---------------------------------------------------------------------------------------

real    0m0,821s
user    0m0,762s
sys     0m0,059s

❯ time ./cloc --only-count-files .
    1404 text files.
     587 unique files.                                          
     868 files ignored.

github.com/AlDanial/cloc v 1.97  T=0.05 s (10684.4 files/s, 0.0 lines/s)
---------------------------------------------------------------------------------------
Language                             files          blank        comment           code
---------------------------------------------------------------------------------------
Assembly                                 2              0              0              0
Bourne Again Shell                      16              0              0              0
Bourne Shell                            40              0              0              0
C                                      271              0              0              0
C/C++ Header                           113              0              0              0
HTML                                     3              0              0              0
Markdown                                 1              0              0              0
PO File                                 39              0              0              0
Perl                                     2              0              0              0
TNSDL                                    3              0              0              0
TeX                                      1              0              0              0
Text                                     4              0              0              0
Windows Module Definition               44              0              0              0
awk                                      1              0              0              0
m4                                      40              0              0              0
make                                     3              0              0              0
sed                                      2              0              0              0
yacc                                     2              0              0              0
---------------------------------------------------------------------------------------
SUM:                                   587              0              0              0
---------------------------------------------------------------------------------------

real    0m0,135s
user    0m0,109s
sys     0m0,024s

[AlDanial]

It's an interesting capability. I'll test & merge this coming weekend.

[AlDanial]

Future work: make --only-count-files work in diff mode also. Currently --only-count-files --diff counts lines too.