Motionscene-merger

- Minor improvement to handling IGNORED_LINES content.

- Published to pypi: https://pypi.org/project/motionscene-merger/
- Reverted default source directory to `res/xml` due to behaviour of Android Studio.

- Content within `<merge>` and `<injected>` tags are now unwrapped (same behaviour as `<MotionScene>`).

- <inject ../> tags are now ignored if they are on a line starting with '<!--' (commented out)

- Add commandline option `--resdir` so you can choose to store your source files
in a different directory than the default `inject`.
This must still be a direct child of the `res` directory.

- Transitive injections are now supported - you can inject content from a file
which has injected content from some other file...etc.

BREAKING CHANGES
- Source files are now placed in their own directory: `res/inject/`
- Source filename prefix changed from `_merge_src_` to `_`
- Merge tag signature has changed
- from `__merge__(target_filename)`
- to `<inject src="target_filename"/>`