new options.strictDimensions for constructor

The new `strictDimensions` option, passed to the constructor, will cause
a section with a dimension with an unknown value to be skipped.
A warning will also be emitted via `console.log`.
strict by default
dropped options.lenientdimensions
bumped version to 1.2.0
Merge pull request #31 from drewfish/unknown-dims

unknown dimension values don't polute master