Vendor target option now accepts an array of vendors.

Vendor filtering and context vendor filtering now works on all aliases.
Fixed issue with nested rules not inheriting.
Made a start on canvas plugin - bitmap generation on top of PHP GD image library.
Added some new boilerplate tags	for command line users.
Fixed small selector overwriting issue.
Slimmed Plugins.ini docs.
Math constants now available in math function expressions.

Just PI for now others can be added if anyone has any use cases.
Moved pseudo element double-colon normalization to an earlier phase to make life easier.
Refactoring

Templating can now interpolate values into string literals.
Selector aliases now use Templating so default values are possible.
Added some plugin API functions to work with the changes to selector aliases.
More work on the canvas plugin.

Added some of the experimental dimension values 'width:min-content' etc. aliases