Define gradle builder and some basic tasks
Keep using the funcall syntax for consistency

The error call means it doesn't matter if we return something bad to the
funcall.
Add gradle to build commands
Fix the android-mode-builder var

It was sort of broken.  Customizing it would break android-mode because
the customize type was string, but the code actually expects it to be a
symbol.
Add custom var for changing root-file
"Fix" docstrings for some functions

So many flycheck warnings!
Add myself as a contributer
Expand doc-string for builder-mode
Add variable to reuse the list of default builders
Use a plist for finding root-file from builder

Instead of storing information in two different variables, maintain a
customizable list of mappings between builder's and root files.

I used a plist because it seems potentially problematic to let multiple
associations exist from builder to root file.  Though I suppose it could
make sense, if we search for each potential root file until we find
one...
Throw an error when builder is not in plist

Instead of passing nil to `locate-dominating-file' which will fail
messily, throw an error with a nicer message.
Fix docstring for builder variable
Fix syntax of the root-file plist
Restructure to avoid bad things with unknown builder

This still isn't totally satisfactory... Android-mode basically just
appears to stop working, and the error message never really gets seen...
Fix `android-build-clean' in gradle build mode
Merge pull request #39 from RadicalZephyr/gradle

Add support for the gradle build system