Allowing p.discretization = 'periodic' to specify @trigcolloc disc.

Also added some documentation describing the various discretization
options.
Merge branch 'fix-chebguiExporter-output' of ssh://github.com/chebfun/chebfun into feature-chebgui-periodic
Adding an periodic EIG demo.
Various changes to make 'periodic' discretization work in Chebgui.
Merge branch 'development' of ssh://github.com/chebfun/chebfun into feature-chebgui-periodic
We now get the titles of plotcoeffs plots automatically!
Ensure we select the correct discretization when exporting to m-files.
Merge branch 'development' of ssh://github.com/chebfun/chebfun into feature-chebgui-periodic
IVP->ivp
Merge branch 'feature-chebgui-periodic' of https://github.com/chebfun/chebfun into feature-chebgui-periodic
Tolerance...
Merge pull request #1306 from chebfun/feature-chebgui-periodic

Making periodic problems work in Chebgui