Merge pull request #36 from ajd4096/master

Add support for M82/M83 absolute/relative extruder positions
Merge branch 'master' into devel
Modified the appearance of the jogging controls with a view to adding finer control
Added controls I want (motors off, fans on/off) - they perhaps should be custom
Started work on adding extrusion control
Merged devel to master, adjusted README a bit.
Added extrusion controls, kept motor and fan controls in general control area as suggested (recurring demand suggests that they definitely aren't something to be added by anyone individually via custom controls), made custom controls always position themselves below the general stuff.
Merge branch 'devel-richardjm'