PHP 5.3 is EOL, and composer no longer supports it.

For Travis CI, the build is also failing outstanding PRs due to
PHP 5.3 requiring Ubuntu Precise (also EOL), whereas the
default image uses uses Ubuntu Trusty.

* Remove outdated version (not needed).
* Update year to last year of significant change or release
  by author.

Closes leafo#603.

Closes leafo#578.

Closes leafo#601.

Same as was done for 'plessc' in 8b6e7a7 (leafo#306).

Closes leafo#610.

See <http://lesscss.org/functions/#color-operations-tint>
and <http://lesscss.org/functions/#color-operations-shade>.

Closes leafo#634.

Two issues:

* The formula was incomplete. This is now fixed.

* The method was returning a float instead of a color array,
  which was used internally for lib_contrast, but was invalid
  as return value to the parser directly.
  The internal utility is now separate from lib_luma.

As side-effect, this also fixes the following for PHP 7.1:
> PHP Warning: A non-numeric value encountered

Closes leafo#626.

PHP 7.1, 7.2 and 7.3 are passing as of 598c96a.

Closes leafo#616.

Fixes leafo#391.
Closes leafo#540.

Closes leafo#605.

Duplicated TLD and trailing slash removal because the variable
is used here: @{url}/bg.png so the url var should be: http://example.com
instead of http://example.com.com/

Closes leafo#566.

I'm already starting to regret this. Obviously, tabs are the only
correct way of indenting code. But alas, PSR2 disagrees and being
different makes the code harder to deal with for those familiar
with PSR2.

I'd be fine with switching to a different popular style preset,
but we shouldn't have our own mix of PSR2 and something else,
so for let's just go all-in on PSR2.

Inspired by MarcusSchwarz#6.

Per <https://secure.php.net/eol.php>
and <https://secure.php.net/supported-versions.php>.

Also because PHPUnit 4.x is on longer supported by upstream.

Ref MarcusSchwarz@cfdd1e2b27.

Follows-up d953e57. Sorry!