Attempt to fix random failures suddenly happening on CircleCI,
likely due to memory issues:
g++: internal compiler error: Killed (program cc1plus)
[skip travis]
[skip azp]
Split header tests accordingly i.e. test core headers as part of
core tests, numeric extension headers as part of numeric tests, etc.
It extends the convention of sub-directories already established in
`include/boost/gil` directory. It is sensible to follow it in other
areas of the source tree (i.e. `test/`, `doc/` and `benchmark/`).
Another important reason to move the tests is to enable removal of
the top-level `Jamfile` with all its definitions of test-specific
requirements.
The top-level `Jamfile` is not advised, especially if it specifies
build requirements like C++ language version.
Those affect non-tests builds e.g. documentation, causing failures
during generation of HTML documentation (leads to missing docs).
Although GCC 4.8 is labelled as C++11 compatible, the reasons are:
* GCC 4.8 is buggy enough to prevent reasonable use of Boost.MP11
* GCC 4.8 is dying
Closes#282
Rename custom variant with gil_ prefix.
Do not define project ID from Jamfile-s as unnecessary.
The project ID-s and build features are global resources, easy to clash.
Add recently added test/ subdirectories to build.
