Clarify description of getMappingPointsWithinMesh

[p-j-smith]

getMappingPointsWithinMesh doesn't get all points that are inside the mesh, only points that are within a specified tolerance of the surface.

A more accurate name would be getMappingPointsOnMesh or getMappingPointsOnSurface.

Event if the name isn't changed to reflect this, it would be good to update the various parts of the description to something:

Update main description:

% GETMAPPINGPOINTSWITHINMESH Returns the indices of the mapping points
% which are located on the surface of the mesh

Add distance units to description of parameters:

% GETMAPPINGPOINTSWITHINMESH accepts the following parameter-value pairs
%   'tol' 0.1 | double
%       - The distance threshold (mm) within which points are considered to be
%         on the surface of the mesh 

Update return description:

% GETMAPPINGPOINTSWITHINMESH Returns the indices of the mapping points
% which are located on the surface of the mesh. The OpenEP function pointStatus.m
% is used to identify these points. The parameter value pairs are passed
% directly onto pointStatus.m