PHP 7 support

[nikic]

BC compatible syntax changes:

• Return type declarations
• Group use declarations
• Null coalesce operator
• Spaceship operator
• Coroutine delegation
• Anonymous classes
• Context sensitive lexer

BC incompatible syntax changes:

• Uniform variable syntax
• Yield operator changes
• Unicode codepoint escape syntax
• Scalar type declarations

API changes:

• Create separate PHP 5 and PHP 7 parsers
• Create wrapping parser that tries using both PHP 5 and PHP 7 in a specified order
• Create factory/builder that creates the proper lexer and parser instances in some simple way
• Document all the things

[avindra]

Linking related issue in other project:

bobthecow/psysh#185

[nikic]

For the record, if you're hitting an error like Cannot use 'String' as class name as it is reserved running on PHP 7: All you need to do is update to version 1.3 and if that doesn't fix it replace your usages of String with String_.

This issue is only about support parsing of PHP 7, not running on PHP 7 (which should already fully work).