Project symbol import from 'ctags'

Summary:
I noticed that documentation said it is possible to have 'ctags' symbol import, so I hacked a quick version. I tested it on Python based project and successfuly imported symbols.

It is limited to classes right now, as the importer script complained about not-unique method names (there are a lot of 'get' & 'post' methods accross classes in my project).

If you would have any feedback about this, I would definetly try to wrap it up for possibly merging into main repository.

Test Plan:
Required 'ctags' tool (ctags.sourceforge.net/) Tested to work with version 5.8+ and didn't work with 3.x.

1. `find . -type f '*.py' | ./generate_ctags_symbols.php > /tmp/symbols`
2. `./import_project_symbols.php` < /tmp/symbols

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: seporaitis, aran, epriestley

Maniphest Tasks: T1034

Differential Revision: https://secure.phabricator.com/D1995

src/docs/userguide/diffusion_symbols.diviner

@@ -27,6 +27,12 @@ Phabricator includes a script which can identify symbols in PHP projects:
 
   ./scripts/symbols/generate_php_symbols.php
 
+Phabricator also includes a script which can identify symbols in any
+programming language that has classes and/or functions, and is supported by
+Exuberant Ctags (http://ctags.sourceforge.net):
+
+  ./scripts/symbols/generate_ctags_symbols.php
+
 If you want to identify symbols from another language, you need to write a
 script which can export them (for example, maybe by parsing a ##ctags## file).