Make C-c C-t work more places

Now, C-c C-t (idris-type-at-point) understands semantic annotations from
the compiler. Thus, it works for annotated text in:

 * REPL output
 * Compiler warnings and errors
 * Info buffers (like the output of C-c C-t)

Requires minor bugfix to ideslave which is submitted to Idris.
Add command for retrieving docs

Now, C-c C-d retrieves the docstring for the identifier under
point. Starting a new pattern-matching definition is rebound to C-c C-s.

Relies on updated Idris compiler to support the command!