Error codes

All service calls in the CTR OS return result codes indicating the
success or failure of the call. Previous to this commit, Citra's HLE
emulation of services and the kernel universally either ignored errors
or returned dummy -1 error codes.

This commit makes an initial effort to provide an infrastructure for
error reporting and propagation which can be use going forward to make
HLE calls accurately return errors as the original system. A few parts
of the code have been updated to use the new system where applicable.

One part of this effort is the definition of the `ResultCode` type,
which provides facilities for constructing and parsing error codes in
the structured format used by the CTR.

The `ResultVal` type builds on `ResultCode` by providing a container for
values returned by function that can report errors. It enforces that
correct error checking will be done on function returns by preventing
the use of the return value if the function returned an error code.

Currently this change is mostly internal since errors are still
suppressed on the ARM<->HLE border, as a temporary compatibility hack.
As functionality is implemented and tested this hack can be eventually
removed.

This prevents them from interfering with other constants defined in
different namespaces.

Added DeleteFile and DeleteDirectory functions to FS:USER and the archives.

Add comment style notes to CONTRIBUTING.md

Closes #215

Add more services and general fixes

in the service's headers

Remove trailing spaces from the entire project

Add static to some variables

Update gitignore to exclude project/editor files

Stretch emulation output to render window and be display density independent

Fix documentation of parameters

directory_sdmc: Fix a signed/unsigned mismatch comparison

system: Get rid of an unnecessary enum typedef

Remove extraneous semicolons

GLFW provides no proper support for this, hence we just allow any window size to be used.

Implementing this function currently is not critical, as we don't perform any configuration changes, yet.

However, the interface is a good starting point for adding this functionality.

The window title is none of the emulation core's business. The GUI code is free to put whatever it wants there.
Providing properly thread-safe window title getters and setters is a mess anyway.