Update README.md (add coverity badge).
[travis] Synchronize.
.travis.yml: remove reference to nsiqcppstyle.
Provide a way to disable tests.

Cf. jrl-umi3218/jrl-cmakemodules#44
coverity: fix some defects.
Update README.md (fix typos).
Add a test for SolverWarning/ResultWithWarnings.
Add a test for GenericSolver.
Use reference to catch exception.
Improve emptiness checking.
util.cc: improve code coverage.
indent.cc: add test.
tests: more code coverage for some specific functions.
problem.hh: improve code coverage.
Fix unused variable warning in test.
Some more code coverage.
Add result to solver print function.
Add an append function to the optimization logger.

For follow-up on #56.
Add even more code coverage.