Tweak .gitignore so git status is clean after checkout and build: - added missing underscore to sample_muxer - added cmake and make related files
Tweak .gitignore so git status is clean after checkout and build:
- added missing underscore to sample_muxer
- added cmake and make related files

Change-Id: Id9a6f12be83d28c95941098b57b61a7a11510f1b

Suvarna1488/webm.libwebm,abwiz0086/webm.libwebm,felipebetancur/libwebm,iniwf/webm.libwebm,kalli123/webm.libwebm,zofuthan/libwebm,webmproject/libwebm,zofuthan/libwebm,webmproject/libwebm,felipebetancur/libwebm,webmproject/libwebm,gshORTON/webm.libwebm