Defined the function Grain::writeStressField
This function writes the stress field due to the grain at points lying
along a line that is specified. It can be used, for example, to
calculate the stress field along a grain boundary.
Added parameter grainStressField
This parameter will indicate when the grain stress field is to be
written.
Defined the function Grain::writeGrainBoundaryStressField
This function calls the function Grain::writeStressField to write the
stress field on different points lying on the grain boundary.
Modified the name of the parameter
Corrected error in function Grain::writeStressField
The vector position increment was calculated wrongly resulting in
positions outside the grains.
Increased resolution for grain boundary stress
Merge branch 'develop' into polycrystal
Pulled changes from develop. These changes were made for writing stresses along the grain boundaries.