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)