Feature request: ctags support

[jonascarpay]

A subcommand to generate a ctags file would give a lightweight and editor-agnostic way to jump-to-definition.

I imagine the simplest possible implementation would collect tags, and then write them in the following format to ./tags or stdout:

!_TAG_FILE_SORTED	1	//
my_tag1	relative/path/to/file1	line_number1
my_tag2	relative/path/to/file2	line_number2
my_tag3	relative/path/to/file3	line_number3
...

[stepchowfun]

Seems like a good idea! I would review a PR for this.