Avoid error when source file cannot be found.
Add PaGMO install script.
before_install: add support for Git dependency branch.
cpp-coveralls: remove deprecated --use-mirrors.
coveralls.io: use lcov instead.
lcov: ignore install_dir.
lcov: fix user-defined ignore rules.
Update README.md
Remove nsiqcppstyle support.

Fix #12
Disable tests for Git dependencies when possible.

Cf. jrl-umi3218/jrl-cmakemodules#44
after_success: check the existence of token/username for GitHub.
after_success: allow coverity upload to fail.
Only use APT for linux.
osx: add Homebrew support.
osx: curl is already provided by Mac OS X.
osx: remove crash-friendly lcov gem.
osx: fix some linux-related clashes.
osx: disable coverity support.
build: fix coverity check.
Update README.md.