Closes #3811

Introducing the curl bug bounty program on hackerone. We now recommend
filing security issues directly in the hackerone ticket system which
only is readable to curl security team members.

Assisted-by: Daniel Gustafsson

Closes #3488

Consistently use one blank line between blocks.

Closes https://github.com/curl/curl/pull/3739

The build logs will be at https://cirrus-ci.com/github/curl/curl

Some tests are currently failing and so disabled for now. The SSH server
isn't starting for the SSH tests due to unsupported options used in its
config file. The DICT server also is failing on startup.

[skip ci]

Ref: https://rawgit.com/ "RawGit has reached the end of its useful life"
Ref: https://news.ycombinator.com/item?id=18202481
Closes https://github.com/curl/curl/pull/3131

- replace tabs with spaces where possible
- remove line ending spaces
- remove double/triple newlines at EOF
- fix a non-UTF-8 character
- cleanup a few indentations/line continuations
  in manual examples

Closes https://github.com/curl/curl/pull/3037

Closes #2913

Closes #2857

Closes #2484

s/off/from

Closes #2300

Closes #2069

rawgit.com asks to use the domain cdn.rawgit.com for production

See #900

Closes #834

It also makes it less readable as plain text, so let's keep this
primarily for github use.

Removed the top ascii art logo, as it looks weird when markdownified.

Attempt to make it look more appealing on github