Remove redundant compiler flag.
Fix project name.
Turn off compiler flags for third-party software.
Fix warnings and reformat code a little bit.
Fix warnings in unit tests.
Rewrite unit test for `PackedPixel` class

Testing PackedPixel with 4 channels as RGBA pixel type is easier to
understand.
Reformat lines of code in `CMakeLists.txt`.
Merge pull request #148 from DO-CV/reduce-compiler-warnings

[MAINT] Reduce compiler warnings.