Fix lint when working on windows

Summary:
Fixes T4395.

Add quotes to ExecFuture strings on Windows to prevent `cmd.exe` from mucking up the command string.

Test Plan: Run `arc lint` on projects using `phpcs`. See everything working like it should.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T4592, T4395

Differential Revision: https://secure.phabricator.com/D9348
Allow triple backticks to be preceded by whitespace.

Summary: Fixes T5264. Allows triple backticks to be preceded by whitespace in a code block. This fixes the display of quoted code blocks, which are regular code blocks prefied with `> `.

Test Plan: Wrote and executed unit tests.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5264

Differential Revision: https://secure.phabricator.com/D9388
Implementation of PhutilLexer for Python

Summary: This appears to be ~1.5-2.0x faster than pygments on my machine, which isn't as good as I was hoping for but will help. (This is ~330 ms for a 4400-line file I chose at random.)

Test Plan: Loaded a Python paste and saw highlights that approximately (or maybe exactly) match the pygments version.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9370