enable alternative units (in, cm, mm)

[j0ono0]

Enable users to input dimensions in physical units.

Might be desirable because aspects of the diagram are intrinsically measured in physical/defined scales:
PCBs are created according to physical dimensions
Diagrams are likely to be printed out on standardized paper sizes (and at dpi higher than screen dpi)

[j0ono0]

good progress is being made!
Currently testing and updating the more complex components.
Details yet to be resolved:

• How to provide default config
• How to provide auto CSS
• What units to include/cater for

[j0ono0]

attempting to roll ALL config into a single file (again). Using a python dict rather than YAML this time.
Initial tests look good.
Features include:

• auto default config for diagrams
• auto switching to reasonable default values for px and mm settings to match a diagrams units.
• auto css file generation
• auto conversion between unit types for CSS (css dimensions need to be in the 'user space units'. Ie, if the diagram is in mm, ALL css measurement values also have to be in mm.