Added the Gander::ParameterizedModel class.
Added copute methods to the ParameterizedModel along with template
arguments in order to define the ModelType.
Merge pull request #10 from goddardl/ParameterizedModel

Parameterized Model
Moved the method for generating points along a curve into Gander::Test::TestTools.
Added the ExponentialCurveFn class.
Added a missing include.
Made the Gander::ErrorFn attributes variable.
Tidied up.
Corrected a comment.
wip