Deprecated: Current working directory on the load path automatically.

Depending on the current working directory makes compiles unpredictable.
The directory of the target file being compiled is automatically on the
load path and this covers all the reasonable use cases.
Upgrade to listen 1.1.x.

This required a substantial rewrite of the watching code because we
needed to move to using absolute values. Additionally, there were a
number of bugs in the watcher that would cause changes in dependencies
to go unnoticed because the Sass load paths were not being watched
for changes. Additionally, the way this code was written, it was trying
to only report a change when the specific file being watched changed.
However, this code never actually worked in practice because the
subdirectory of the changed file wasn't necessarily the directory of the
watched file, and even when it was, the way it was reported from the
listener caused the subdirectory to be blank. There was also some very
bad things that would occur if the sass cache directory was a sub
directory of a watched directory.
When watching, delete sourcemap files if they have been generated and the corresponding sass file has been removed.
Make travisci happy.
Remove unnecessary deprecated importers.

If a deprecated importer is found on the load path we remove it if
there is a non-deprecated importer that points at the same filesystem
root.
Address some code review comments.
Change ouput for overwrite to write

Because the file is already written to disk, we cannot detect the
difference between created and overwritten.
Delegate paths and filenaming conventions for watching to importers.

Importers should be the single point of knowledge about where files
are coming from. As such, there are two new methods on Importers::Base
which allow an importer to specify what directories to watch and to
control whether a file from those directories should trigger a
recompile.

This patch also adds tests to the watcher code by creating a mock
listener and stubbing out the methods that do the action changes
when compilation and file manipulation occurs.
Address code review comments.