Rename HandlerConfiguration.cc/hh to handler_configuration.cc/hh
Adopt STL naming convention in handler_configuration.cc/hh
Rename HandlerConfigurationApi.cc/hh to handler_configuration_api.cc/hh
Adopt STL naming convention in handler_configuration_api.cc/hh
Support long file names in checkheaderinclude.sh

We have a hard limit on line length (79 characters per line), but
include guards enforced by the checkheaderinclude.sh script do not fit
in the limit if the source file name is too long. Since we are not going
to remove the limit, include guards should be truncated if too long. The
checkheaderinclude.sh script now has to accept such truncated guards.

This commit overhauls the script not only to support the long lines but
also for more user-friendly error messages.
Adopt STL naming convention in SignalErrorCategory.cc/hh
Adopt STL naming convention in SignalErrorCode.hh
Rename SignalNumber to signal_number
Rename SignalNumberSet.hh to signal_number_set.hh
Adopt STL naming convention in signal_number_set.hh
Adopt STL naming convention in signal_number_set_test_helper.hh
Remove *Test from .gitignore
Merge pull request #134 from magicant/refactor/rename

Adopt STL naming convention in sesh::os::signaling