Support etags

[lf-]

I don't want to write the code for this:

• The format sucks: you basically have to write each file's tags into a buffer before writing it out to disk because there's an ascii count of the number of bytes for each file's section. You also just have to collect a lot more data that has not much reason to actually be needed.
• Supporting it would necessitate the program do more work.
• I don't use Emacs.

Useful info on the format:
https://stackoverflow.com/questions/1990579/understanding-the-ctags-e-file-format-ctags-for-emacs
https://en.wikipedia.org/wiki/Ctags#Etags_2

I might look at this at a future date assuming someone wants it.