Add Tizen Filesystem API.

This commit implements most of the Tizen Filesystem API.

Some things were intentionally left unimplemented, such as listing and
obtaining stoarage information. These will be implemented as soon as the
need to pass all TCT tests arise.

File I/O works, as evidenced by the new filesystem.html example (a crude
text editor) -- although this example doesn't showcase the whole API.
Merge pull request #148 from lpereira/filesystem-api

Add Tizen Filesystem API.