This commit passes the mutated source to the template handler as a
parameter and deprecates the old handlers. Old handlers required that
templates contain a reference to mutated source code, but we would like
to make template objects "read only". This change lets the template
remain "read only" while still giving template handlers access to the
source code after mutations.
The current implementation can't handle some special cases of oddly-formatted Ruby. Now we are able to detect them:
* Multi-line arguments on the `render` call
* Strings containing quotes, e.g. `"something's wrong"`
* Multiple kinds of identifiers - instance variables, class variables and globals
* Method chains as arguments for the `render` call
Also, this fix reduces the rate of "false positives" which showed up when we had calls/access to identifiers containing `render`, like `surrender` and `rendering`.
