Replace the bash selftest plumbing with CTest.
To use the selftests, build with -DLWS_WITH_MINIMAL_EXAMPLES=1
and `CTEST_OUTPUT_ON_FAILURE=1 make test` or just
`make test`.
To disable tests that require internet access, also give
-DLWS_CTEST_INTERNET_AVAILABLE=0
Remove travis and appveyor scripts on master.
Remove travis and appveyor decals on README.md.
