Autocomplete global symbol table generator app

Autocomplete global symbol table generator app

Summary:
Create a program, global_index_builder, that can scan WWW and generate a saved-state containing autocomplete global symbols.

An autocomplete global is:
* A name (string)
* A kind (integer, indicating class, interface, enum, trait, unknown, mixed, function, or typedef)

The program produces:
* A SQLite database with symbols and kinds.
* A text file written as one symbol per line followed by a space followed by the integer number of the kind

Syntax:
```
$ global_index_builder --sqlite ./www.autocomplete.db --text ./www.autocomplete.txt ~/www
Building global symbol index for [/data/users/tspence/www-hg/]
Scanning repository /data/users/tspence/www-hg/...  [11.0 secs]
Parsing 1536385 files...  [87.5 secs]
Writing 2209147 symbols to sqlite...  [66.7 secs]
Writing 2209147 symbols to text...  [41.0 secs]

Global Index Built successfully: [206.5 secs]
```

Differential Revision: D14645751

fbshipit-source-id: e35124a8451a2ad5d019f71524cd58d72f108f4d