Include information about how to deal with lint warnings and suppress
`clang-format` reformatting of blocks of code.
Move information only relevant to developers from the README.md to the
CONTRIBUTING.md document.
Closes#2901
This changes implements two new make targets: `style` and `style-all`. These
make it easy to ensure that a change conforms to the project style guides for
C++ and fish code.
Fixes#571