Add a verbosity level for reporting activity

[kbenoit]

How about: verbosity = c(1, 0, 2, 3)

which means:

• 1 (default) report something like:

  Read a total of 16 files.

• 0 no reports at all
• 2 detailed report

  Read: 
    5 Word documents
    18 text files
    6 HTML documents
   a total of 29 files.

• 3 most detailed report

  Reading: 
    ~/texts/document_1.txt
    ~/texts/document_2.txt
    ~/texts/document3.pdf
    ...
  a total of 103 files.