Issue 272 - removing the dependency on pango and cairo

[sminez]

See #272 for the details for this one. This work was initially done as an MVP in sminez/x11-draw but there are a number of modifications that are required from the code that is there in order to wire it into the statusbar widget behaviour and layout.

Breaking changes

This will be a breaking change for the current API around the status bar as a number of things are tidied up where elements of the cairo and pango APIs had bled through to the public API of penrose_ui (in particular, using floats for offsets and colour representation...).

• A Draw only supports a single primary font (fontconfig is used to find a suitable fallback for missing glyphs)
• Method APIs on the Draw and Context structs have been modified to no longer bleed through implementation details from pango and cairo (unless you implemented your own fully custom Widget this should not affect end users)
• Context is now a reference type with a lifetime, providing a view on the surface assigned to a given window.
• TextStyle no longer contains font and point size fields: these are set on the Draw
• TextStyle and individual Widget padding, height and offset fields are now u32 not f64
• TextStyle is now a Copy type and is passed by value not by reference for all widgets and the status bar
• Constructing a status bar now requires the font and point size as arguments (given that they have been removed from TextStyle.

One additional breaking change is that the status bar (and a Draw in general) will only support a single font. The examples provided previously only ever used a single font and behaviour when trying to use multiple fonts has never worked correctly so while this is a breaking API change it's not really a loss in (usable) functionality.

Version bump and alignment

There are some changes to the main penrose crate as well so I'm taking this as an opportunity to align the version numbers of penrose and the additional crates going forward. The APIs between penrose_ui / penrose_keysyms and penrose will only be supported for matching version numbers going forward.