Improve nested module calls in grdimage

Add docs for coast and grdimage

Expand several complex options to key/val syntax

Also add galleries for projections and other examples.

General improvments of the plotting modules

Add automatic legends, plot multi lines at once, etc.

Greatly expand the number of submodules

Add more documentation but above all, many options and sub-options have been expanded to use keywords.

Port all basic GMT programs to the "By modules" mechanism

Almost all basic modules were ported. Left behind gmtmath and grdmath due to complexity and a couple others (like grdconvert) because it doesn't make much sense to port them too.

Fix deprecations on OSX and linux

v0.4.1

Add the 4 basic operations to GRDgrid types.

Julia 0.7 ready

Drop support to Julia versions prior to 0.7

Solve issues with Julia version require

v0.3.0

Expand a little about some options in the examples.

Fix issue with GMT.jl file not exporting some correct function names

v0.2.1

Swap to 5

Add a By module name upper lever interface

v0.2.0

Add GMT description