Implement clang-static-analyzer lint

[matt-chan]

This is a slow linter, but rather good at catching C/C++ errors:
https://clang-analyzer.llvm.org/

It would be nice to augment cppcheck with this.

[tovrstra]

This is quite an advanced technique and I guess we cannot treat it as just any other linter. You essentially have to build the code with analyzing compilers, normally using debug settings. This can be done by prefixing any command that would invoke a compiler by scan-build, e.g. scan-build make. This generates a html report but also xml "plist" files can be generated. These can then be post-processed, like we do with the output of other linters. (I'd have to get some experience with the analyzer first to see how this can be done exactly.)

clang is available on travis by default, so we do not need conda packages for it.