New makefile component_wrapper.mk allows some variables to be set
before component.mk is evaluated. This properly fixes problems with
sdkconfig being hard to access in all phases of the build.
Including component_common.mk is no longer necessary and will print a
deprecation warning for components which use it.
1. change the description of Makefile.projbuild
2. remove the license header in the API document
3. add private inlcuding header code in the components file
Angus Gratton