External linters can now specify a version requirement.

Summary:
Linters can now use the version configuration value to specify the required
version of the external binary. The version number may be prefixed with <, <=,

, >=, or = to specify the version comparison operator (default: =).

PHP's native version_compare() function is used to perform the comparison.

Fixes T4954.

Test Plan: Tested against a sample of external linters.

Reviewers: joshuaspence, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, joshuaspence

Projects: #lint

Maniphest Tasks: T4954

Differential Revision: https://secure.phabricator.com/D14298