- also update two URLs outside of docs/examples
- fix spelling of filename persistant.c
- fix three long lines that started failing checksrc.pl

Closes https://github.com/curl/curl/pull/3036

Closes #2948

Also suppress length argument of curl_mime_name() (names are always
zero-terminated).

and some minor whitespace fixes

Additional mime-specific tests.
Existing tests updated to reflect small differences (Expect: 100-continue,
data size change due to empty lines, etc).
Option -F headers= keyword added to tests.
test1135 disabled until the entry point order change is resolved.
New example smtp-mime.
Examples postit2 and multi-post converted from form API to mime API.

In order to make the code style more uniform everywhere

All plain C examples now (mostly) adhere to the curl code style. While
they are only examples, they had diverted so much and contained all
sorts of different mixed code styles by now. Having them use a unified
style helps users and readability. Also, as they get copy-and-pasted
widely by users, making sure they're clean and nice is a good idea.

573 checksrc warnings were addressed.