A library is usually expected to be built in a folder /build at
its root. Whenever this repository is added as a submodule of
another project and compiled, git shows all the generated files as
changes. To suppress those git messages, this ignores the build
folder.
This adds the -fprofile-arcs and -ftest-coverage options when compiling
the source code for the static library. Those same options must then be
used when linking the static library into an executable. This updates
Makefile.in to remove and .gitignore to ignore the files generated when
testing coverage.
