Split Parser into two generators

[halaxa]

1. Rename Lexer to Tokens
2. Split Parser into 2 parts
   1. SytnaxCheckedTokens - Will iterate Tokens and will only check syntax of tokens and yield it along
   2. PhpItems - Will iterate SyntaxCheckedTokens and yield php structures

It makes possible to skip syntax checking (to gain speed where applicable) very easilly. User can simply remove SyntaxCheckedTokens from generator stack.

It will also pave way to #36.

[halaxa]

This will probably be solved differently. Closing for now.