Automatically run appropriate linters

[baileyparker]

• Valgrind (installed) for C/C++ (requires mucking with simple_test.runner)
  • Probably want to run as part of regular tests (run each test twice, second time for valgrind)
  • Probably want to send valgrind output to file (to not muck with stderr of compiler): valgrind: --log-filename="path/to/tmp/file"
• go vet (installed), go fmt (installed), golint (not installed)
• checkstyle (installed) for java with attached config: checkstyle.xml.gz (gzipped because GitHub doesn't support uploading XMLs, really GitHub?)
• flake8 (installed) for Python

Probably need a mechanism for automatically detecting language (exclude integration_test dir!). Lists taken from: https://github.com/github/linguist/blob/master/lib/linguist/languages.yml

• Python: *.py
• C/C++: *.c, *.cpp, *.c++, *.cc, *.cxx, *.h, *.h++, *.hh, *.hpp, *.hxx
• Java: *.java
• Go: *.go

Also need flags to force language detection and disable this feature (part of making bin/run_harness a python script for #17).