Move php7-v2 to master

[Totktonada]

It seems that community prefer php7 and now we can obsolete php5 support. I propose to move current master (php5) into the separate branch and move php7-v2 branch (force-push or merge, don't sure) to master.

Packages then will be build for php7, so #117 (and #136) will be fixed.

We need to elaborate what additional work is needed here: update docker images and so on.

@bigbes Can you please comment?

[Totktonada]

Blocked on:

• PHP 7.3 support (Add PHP 7.3 support #139).
• PHP 7.4 support (tarantool-php with php 7.4 #150).
• RPM/Deb packages (Deploy PHP7 Deb/RPM packages #117).

[Totktonada]

As part of this issue we should ensure that all commits into master branch since php7-v2 forking point are either unrelevant or reflected in the php7-v2 branch.

What to inspect:

$ git merge-base origin/master origin/php7-v2
61b9d7bc15d78e210b58e2a16feecdb3982923a9
$ git log 61b9d7bc15d78e210b58e2a16feecdb3982923a9..origin/master

[Totktonada]

• Created new php5 branch, which is even with current master (03fc9fe, 0.1.0-49-g03fc9fe).
• Force-pushed master branch with latest php7-v2 commit (ad221f7, 0.3.2-39-gad221f7).
• Changed target from php7-v2 to master in open PRs.

Nothing more to do here. We should carefully look at README (whether it is actual) as follow up. See also PR #129.