perlport: major overhaul

perlport: major overhaul

- hyperlink function names
- hyperlink variable names
- hyperlink module names
- hyperlink $Config{...} entries
- hyperlink some C function names
- hyperlink ``/qx, tr///, bitwise operators, BEGIN
- remove bareword filehandles from examples
- remove 2-arg open from examples
- recommend 3-arg open always
- clean up weird formatting and use \Q \E in $Config{_exe} example
- mention Time::Piece (a core module) for date parsing (-> strptime)
- prefer 'use' for loading modules unless there's a reason to 'require'
- remove paragraph about using 'use bytes' to indicate that your source
  code is in some native 8-bit encoding (that's not what 'use bytes'
  does and its use is "strongly discouraged" anyway)
- consistently use 2 spaces after a period
- consistently spell $Config{foo} as $Config{foo}, not $Config{'foo'}
  sometimes
- fix some POD markup
- remove reference to 'pl2cmd' because I've never heard of it and all
  search results on the web point back to copies of perlport
- remove claim that binmode is a no-op on non-windows systems (that
  hasn't been true since the introduction of I/O layers and Unicode text
  files)
- realign some tables
- don't describe sets of characters as "matching tr/...//" because tr///
  isn't really a matching operator (it can be used to *count*, but
  that's not obvious to most people)
- remove nonsensical VOS example that claims to check the architecture
  by examining @INC but doesn't actually use @INC or check the
  architecture
- 'chown' can't be both "not implemented" and "implemented, but does
  nothing" on Win32
- remove "semantics of raise()" wording from 'kill' because it's unclear
  (raise doesn't send a signal to another process anyway)
- remove 'sockatmark' entry because there is no such built-in function
  (the closest thing I can find is IO::Socket->atmark, which already
  carries appropriate portability warnings)
- in 'stat', consistently refer to fields by their names from
  perlfunc/stat
- add myself to list of contributors