usage message changes

[kberry]

1) It is customary to output a few words about what a program does in its usage message.

--- detex-src/detex.l   (revision 64397)
+++ detex-src/detex.l   (working copy)
@@ -1093,7 +1111,8 @@ UsageExit(void)
 {
        (void)printf("\n%s [ -clnrstw1 ] [ -e environment-list ] [ filename[.tex] ... ]\n",
                sbProgName);
-       puts("  -c  echo LaTeX \\cite, \\ref, and \\pageref values\n  \
+       puts("Strip (La)TeX commands from the input.\n\n  \
+                -c  echo LaTeX \\cite, \\ref, and \\pageref values\n  \
 -e  <env-list> list of LaTeX environments to ignore\n  \
 -l  force latex mode\n  \
 -n  do not follow \\input, \\include and \\subfile\n  \

2) It is useful to output the program home url in the help message. And can only help to output the version number too.

--- detex-src/detex.l   (revision 64397)
+++ detex-src/detex.l   (working copy)
@@ -1093,7 +1111,8 @@ UsageExit(void)
 {
        (void)printf("\n%s [ -clnrstw1 ] [ -e environment-list ] [ filename[.tex] ... ]\n",
                sbProgName);
-       puts("  -c  echo LaTeX \\cite, \\ref, and \\pageref values\n  \
+       puts("Strip (La)TeX commands from the input.\n\n  \
+-c  echo LaTeX \\cite, \\ref, and \\pageref values\n  \
 -e  <env-list> list of LaTeX environments to ignore\n  \
 -l  force latex mode\n  \
 -n  do not follow \\input, \\include and \\subfile\n  \
@@ -1102,7 +1121,10 @@ UsageExit(void)
 -t  force tex mode\n  \
 -w  word only output\n  \
 -1  outputs the original file name and line number in the beginning of each line\n  \
--v  show program version and exit");
+-v  show program version and exit\n\
+\n\
+opendetex home page: https://github.com/pkubowicz/opendetex");
+       (void)printf("opendetex version %s\n", VERSION);
        exit(0);
 }

@@ -1113,7 +1135,6 @@ UsageExit(void)
 void
 VersionExit(void)
 {
-       (void)printf("\nOpenDetex version %s\nhttps://github.com/pkubowicz/opendetex\n",
-               VERSION);
+       (void)printf("\nopendetex version %s\n", VERSION);
        exit(0);
 }