New Section::filter method and new config check
Validation result is always a Section

Validation result is always a Section, even if validation was
successful. In ConfigObj successful validation returns None.
New README.md
Executable name changed
Build of static and/or shared libraries
Option message modified
sequence.h -> tuple.h, list.h
mapping.h -> dict.h, section.h
config.h -> config.h, configspec.h, vconfig.h
scalar.h -> scalar, numeric, int, float, bool, str
object.h -> base, stateless, none, undefined
Prefer linking static libraries by default
argparser_common.h -> argparser_common.h, error.h
Partial support for cccc
internal_op -> private_utils
Wrapping std exceptions

Closes #35
ArgGroup vector added to ArgParser
Argument groups added to help
Added test with groups
Mutually exclusive groups