Improve tag generation performance. Details:

Performance fixes (LOLSPEED [tm]):

- Set escript to run in compiled mode
- Introduce precompiled regexes
- Use iolists/binaries instead of "strings"
- Scan files with multiline regexes instead
  of sequential line-by-line reads

Various minor fixes:

- Improve function detection regex
- Change ETS table structure, so even more actual tags
  are now detected
- Replace ets:foldl dump with sort and tab2list combo
  (seems tenderly faster on my machine)
Add 'erl' extension to the tag generating escript

... so github won't think it's perl and whatnot.
Merge pull request #2 from aerosol/master

Speed up tag generation