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).
(cherry picked from develop branch commit 4ed7701b47)
The build variants enable group of checks offered by clang
UndefinedBehaviorSanitizer detector.
Add sanitizers suppression file in .ci/blacklist.supp based on
copy of the file from Boost.Beast.
Update Travis CI:
- Add .ci/build-and-test.sh script as handy proxy for b2 command.
- Add build jobs for each of the three new UBSan variants.
- Display COMPILER and VARIANT first as these two are most important
details while inspecting the build matrix
(TOOLSET can be derived from COMPILER).
