Support PHP7 error exceptions everywhere

[danez]

This handles error exceptions in all places and also replace \Error with \Throwable.

This is a breaking change as the API for the interface PromiseAdapter changes, but otherwise there is now way in catching php7 errors that might happen in the Promise.

[vladar]

I'd really like to accept this PR. Minor breaks are ok for next major version, but this PR breaks every PHP version older than 7.0+. And we must still support previous PHP versions. Can you try running tests on PHP5.6 and fix failures?

[danez]

It was meant to be bc, besides the change of the interface. I had #126 before which broke php <7, this should have been the fixed version.
Let me check.

[danez]

Okay I fixed it.

[coveralls]

Coverage decreased (-0.03%) to 93.47% when pulling 2a992fa on danez:throwable into e7cde5e on webonyx:master.

[vladar]

Thanks! I'll merge it when I start working on next major version

[vladar]

@danez Can you change target branch of this PR from master to v10.0 ?

[danez]

Done

[coveralls]

Coverage decreased (-0.03%) to 93.447% when pulling 65ef159 on danez:throwable into a0657b7 on webonyx:v0.10.