Add linting

[alexander-novo]

There are a few style guidelines (#5) that can't be enforced by formatting alone, since they're outside the purview of formatting. For example: identifier naming schemes and error handling. These can be checked by a linter, though, and linting in general isn't a bad idea in a C++ codebase. If we're requiring clang-format as a dev dependency, then we can use clang-tidy, which is also included in clang. This can be added to precommit hooks (#33) and CI (#25).