This PR attempts to introduce a level of incremental parsing for the Tolerant PHP Parser.

Currently:

• The user types $, a, b and c.
• IDE sends 4 completion requests to Phpactor
• Phpactor will re-prase the document for each request

With this change two strategies are employed to avoid reparsing:

In Token Changes

• The user types $, a, b and c
• Phactor sees that the c edit is within a VariableName token and that
  when the edit is applied to the previous token we go from $ab to $abc
  and $abc is also a variable name token so we can just update it.

Compound Node Edits

• User changes a statement within a compound node (i.e. within { } braces)
• Phactor sees this is a change to a statement
• Extracts the text from where the edited statement starts
• Transposes the text edit to the extracted text
• Applies the text edit
• Grafts the newly parsed AST into the old tree
• Reindexes the tokens.

Affect

In certain situations this can result in a 2x or more speed increase, especially in large, complex, files because:

• Parsing time is 10x faster if an incremental update can be found.
• The unchanged node instances remain the same, meaning the cache can kick-in for type infrormation.

Things become more difficult if more context is required (e.g. public function foo is meaningless without the surrounding class construct) but in those cases they could, I suppose, be artificially supported.

TODO:

• Document cache no longer cleared on update - document cache is used for diagnostics, so need to use separate caches.
• WorkspaceListner
• Diagnostics are no longer cleared on update (they were cleared via. the document cache clearing)
• Document cache not purged on goto definition (... ? e.g. after generaitng a missing method and jumping to it).
• Diagnostics are not updated n realtime (event is not captured - text is not available)