Emacs support, allow taking files from stdin, bug fixes

[drvink]

New features:

• Emacs tags format support
• Ability to take the list of files from stdin, either newline or NUL separated
• Support for generating tags for module-less files (i.e. an implicit module Main (main) where)

Bug fixes:

• A tag is no longer generated for the name of the file; it causes some problems for Emacs and the other Haskell tags generators don't do it (for either Vim or Emacs)
• Tags for operators/symbols are now included--you seemed to intentionally not be doing this, though; was there a reason?

Internal stuff:

• Switched from cmdargs to optparse-applicative; it has a much nicer API
• Cleaned up the source (wrapped long lines, made hlint shut up)

[luqui]

Uploaded, thanks!

[drvink]

Thanks for accepting it! :) I should have some more changes coming soon.