added COMPATIBILITY.md to track compatibility against LinkedIn fork
bringing the behavior and style of `Context`'s `get` and `get_path` into line with the LinkedIn form:
* `get_path` and `get` now proxy a univsersal `_get`
* the behavior now walks up a tree, so dirty hacks to access variables outside scope are not necessary.  ie : {#A.B} name in B={name} {#A} name in A: {name} {/A} {/A.B}