Improve LSC example

[danieljfarrell]

The LSC example should be made a bit more user friendly.

• Generalise to an LSC not axis aligned.
• Need to improve, and perhase formalise, the way facets are assigned to intersection points.

[danieljfarrell]

Have started this on this branch https://github.com/danieljfarrell/pvtrace/tree/dev/lsc-device

See, https://github.com/danieljfarrell/pvtrace/blob/dev/lsc-device/pvtrace/device/lsc.py

[danieljfarrell]

LSC code has been merged into master in release 2.1.3