C man, perldoc and misc improvements

Integrate Magnus Woldrich's perldoc.vim and activate it for perldocs.

Strip leading blank lines from man pages so that the C syntax
highlighting works for C functions in man.vim.

Read target file with ":silent! e ${filename}" instead of as an arg, so
that modeline errors and the like are suppressed.

TODO:

 * there are many problems with perldoc.vim that need to be addressed in
   the future:

   1. it does not highlight section names

   2. it highlights perl keywords in text, which are often regular words

   3. it sometimes highlights whole paragraphs

 * see if there are any other useful things in vimpager-perlmod to
   integrate here

 * we may want to fork man.vim and do C highlighting for sections other
   than then SYNOPSIS as well, and support man pages for other
   programming languages too.

 * somewhere along the way, we lost the ability to open multiple files,
   this is why the ":silent e" hack was possible, but it would be good
   to restore the support for opening multiple files in the pager at
   some point.