Generate a tags file for navigation while editing

[amartini51]

The output uses using the POSIX ctags syntax, and enables "jump to definition" for DocC links and for syntactic categories in the formal grammar. From testing with a few different editors, here's what I saw:

• In Vim, you have to configure setlocal iskeyword+=#,:,- to allow those characters as part a tag. Then both links and grammar works. Classic vi supports tag files, but doesn't have iskeyword, so other vi-like editors might not be able to follow tags.
• In BBedit, links work without configuration changes. I wasn't able to get grammar to work, likely because it doesn't consider - as part of a tag.
• Emacs has support for tags files, but it seems to need a module or configuration change to handle the ctags syntax instead of its preferred etags syntax.
• Xcode uses its own indexing for navigation, not a tags file.

Marking this as a draft for now. I'd like to consider rewriting the script in Swift.