Add macro expansion on hover

[nobodywasishere]

When enabled, when the cursor hovers over a macro, the file/line is sent to crystal tool expand and the results are returned in a hover.

Closes #4.

Simple example

Macros defined in src/mlcsim/transcoder.cr:

Main file set to src/mlcsim.cr:

Macro expansion on hover in spec/mlcsim/matrix_spec.cr:

[nobodywasishere]

I'm thinking about adding to this the option to right click on a macro and click an option like "Show macro expansion" which would show the output in an output pane, as an alternative to hovering.

[nobodywasishere]

Added!

[nobodywasishere]

So this probably won't be merged but rather re-implemented for the rewrite. With that, I think I'm only going to have it as a right click option as it's something that's only need here or there, versus type information (which is what hover is currently used for).

[nobodywasishere]

This will be implemented with the rewrite.