WIP: Autolink URLs in blobs and diffs

Extracted from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4121.

Contains three attempts/approaches at autolinking:

• 134c848c
• 86c54979
• 798d3289

None of these have acceptable performance.

To do

• Make sure blob rendering performance doesn't suffer dramatically
• Don't run pre-processing pipeline, because this may break the highlighting

mentioned in merge request !4121 (closed)

mentioned in merge request !11224 (merged)

added 324 commits

• 798d3289...ec1a3c09 - 319 commits from branch master
• e82010da - Make AutolinkFilter smarter about trailing punctuation
• f678137b - Autolink URLs and emails in blobs and diffs
• 625ce63c - Update specs
• ed6cbde2 - Autolink all of the highlighted text at once
• 5bcdc435 - Autolink the raw text and “transfer” the found links to the highlighted text

Compare with previous version

added Platform ~159098 labels