Bump to Polylang Pro 3.7.3.

Fixed required php version

Update stubs for version 3.4.3

Merge pull request #7 from szepeviktor/patch-1

Fix generator in README

Bump to Polylang 3.3.1.

Bump to Polylang 3.3.

Remove composer.lock

Update stubs for the version 3.1.2

Not sure how the PLL_Lingotek class was previously removed from the
stubs of the version 3.1 stubs.

Updated stubs to 3.1

Add readme