Adjusted _plot_limb to use the map.center property if defined.
Added draw_limb and draw_grid to compositie map class.
Implemented in such a way that the user selects a map index to use for the
plotting of the limb / grid, whereby it calls the method in that map.
Modified Import Warning for C extension
Remove patches import
Modified comp_map.draw_limb to find first map with rsun attr.

Also forcibly set zorder in map.draw_limb() to make it on top of comp map
Added default index code to draw_grid.

Same as last, also added zorder=100 to map.draw_grid()
Changed C extention print to ImportWarning
More changes to index
Added exceptions to composite map draw_grid + limb
Changed Crotate fail behaviour: issue #390
Changed warning to not raise error.
Chenged ImportWarning to Warning as import Warning is ignored by default.
Added a notes section to map.rotate() docstring.
Modified troubleshooting section in docs
Tidying up docs
Remove debugging if True:
built--> compiled
Merge pull request #384 from Cadair/staging

Adding Composite Map draw_limb and draw_grid.