Make `#` header detection more strict

Summary:
Ref T5102. Require a space after a single `#` at the beginning of a line to possibly trigger header behavior.

This prevents conflicts with `#projects` and some normal text beginning with `#`.

Test Plan: Added unit test.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: pieter, epriestley

Maniphest Tasks: T5102

Differential Revision: https://secure.phabricator.com/D10151
Allow Remarkup list items to have multiple paragraphs

Summary: Ref T4939.

Test Plan: Added unit tests.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4939

Differential Revision: https://secure.phabricator.com/D10154
Remove some leftover `@group` annotations

Summary: These were leftover after D9856.

Test Plan: Eyeball it.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10147
Rename `AphrontQueryException` subclasses

Summary: Ref T5655. Rename `AphrontQueryException` sublasses for consistency. I'm not a huge fan of all of resulting class names, but they do feel more consistent.

Test Plan: Ram `arc lint` and `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10149
Rename `PhutilKeyValueCache` subclasses

Summary: Ref T5655. Rename `PhutilKeyValueCache` subclasses for consistency. I intentionally left `PhutilKeyValueCacheNamespace`, `PhutilKeyValueCacheProfiler`, `PhutilKeyValueCacheProxy` and `PhutilKeyValueCacheStack` because these seem to be special cases.

Test Plan: `arc lint` and `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10155
Rename test class

Summary: Ref T5655. Rename `PhutilPHTTestCase` to `PhutilPhtTestCase` for consistency with the method under test (`pht`).

Test Plan: `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10158
Rename `PhutilParserGeneratorException` subclasses

Summary: Ref T5655. Rename `PhutilParserGeneratorException` subclasses for consistency.

Test Plan: `arc lint` and `arc unit`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10159