Partial variable in include tag

Implements #2142

The fix is simply adding to the `VARIABLE_SYNTAX` regex. I changed it so that the "variable" capture group would also capture any characters before `{{` and after `}}`. 


The regex bit that I added to the beginning is `[^{]*` which selects anything except for `{` and the bit that I ended to the end is `[^\s}]*` to match anything except for `}` or whitespace (in case it tries to greedily match the params part).