Add assertions to every test in libphutil/

Summary: Ref T4570. Add an assertion to all tests which pass by not exploding, so we can fail tests which make no assertions.

Test Plan: `arc unit --everything` with the test engine set to fail on no assertions.

Reviewers: leebyron, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4570

Differential Revision: https://secure.phabricator.com/D8435
Utilize `assertFalse` and `assertTrue` methods.

Summary:
Ref D8460.

Use $this->assertFalse(...) and $this->assertTrue(...) instead of $this->assertEqual(false, ...) and $this->assertEqual(true, ...) respectively.

Test Plan: `arc unit`

Reviewers: epriestley, #blessed_reviewers

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8462
Update some libphutil docs

Summary: Improve organization and content of some documentation.

Test Plan: Regenerated and examined docs.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D8479