Changes the mapinfo so that the mapped data is writable

Opening a new MR because I can't push to @dkl's repository to update !16 (closed):

The Problem is, that in the current state it is not easily possible to edit the buffer data in a gstreamer python element since you get a copy of the reals buffer.

This patch overrides the mapinfo and the function generating it in a way so that mapinfo.data is now a memoryview pointing to the real buffer. Depending on the flags given for this buffer the memoryview is r/w.

Fixing following issue #13 (closed)

I fixed a build issue and removed a few unused variables.

mentioned in merge request !16 (closed)

added 2 commits

• acb2da66 - 1 commit from branch gstreamer:master
• b46fdcfc - Changes the mapinfo so that the mapped data is writable

Compare with previous version

Rebased and fixed a few whitespace issues.

@slomo, @thiblahute, please let me know if there are more changes required.

added 1 commit

• d0405683 - Apply suggestion to gi/overrides/gstmodule.c

Compare with previous version

added 1 commit

• 2af4b29e - Apply suggestion to gi/overrides/gstmodule.c

Compare with previous version

added 1 commit

• 41e70093 - Apply suggestion to gi/overrides/gstmodule.c

Compare with previous version

added 1 commit

• 81d38269 - Apply suggestion to gi/overrides/gstmodule.c

Compare with previous version