ref #25 - the dreaded tabs-to-spaces conversion
ref #25 - the dreaded file split and fixing phpcs warnings/errors
update travis config
rename op_ methods (PSR2)
rename lib_ methods (PSR2)
bump semver to 0.1.0; update docs
fixes #70 - expression evaluation

Note: it's closer to scss 3.3.14 / 3.4.0rc3 behaviour than 3.2.19
fix color division (see 3.2.19/3.3,14/3.4.0rc3)