Add createFromFormat static method to CarbonInterval

[xfudox]

Added createFromFormat method to CarbonInterval's core for #1918 .

Useful to handle time interval strings like MySQL time field (e.g.: '10:20:00'):
E.g.:

CarbonInterval::createFromFormat('H:i:s', '10:20:00')

is equivalent to:

list($hours, $minutes, $seconds) = explode(':', '10:20:00');
new CarbonInterval(0, 0, 0, 0, $hours, $minutes, $seconds);

or

CarbonInterval::hours($hours)->minutes($minutes)->seconds($seconds);

[kylekatarnls]

Hi @xfudox, thanks for your PR, would you mind please adding unit tests for your feature.

See as an example:
make test:
https://github.com/briannesbitt/Carbon/blob/master/tests/CarbonInterval/ConstructTest.php#L283
or __construct test:
https://github.com/briannesbitt/Carbon/blob/master/tests/CarbonInterval/ConstructTest.php#L21

Thanks

[kylekatarnls]

• Unit tests
• Fix PHPDoc

[kylekatarnls]

Hi @xfudox I had no time to fix the PHPDoc and add unit tests, so I postponed this for version 2.27. Thanks for your understanding.

[xfudox]

Yeah, sorry for I'm late, I've very little free time to work on this recently, hope to fix this asap.

[kylekatarnls]

Hi @xfudox thanks for unit tests and doc. The unit tests are not passing in Travis. Can you have a look?

[xfudox]

Yeah @kylekatarnls , I'll take a look asap.

[kylekatarnls]

Obviously, my solution (the macro proposition made in the issue) will only work with hours, not for day/month/year, so we actually need to parse the format in a custom way. I take the assignee to propose something else.

Changes done myself

[kylekatarnls]

Hi @xfudox can you check the new implementation?