Updates Matlab definition to allow colons within cell arrays

Previously, colons were specifically not allowed within a cell array ({}), however there are many valid use cases where a colon can be placed within curly brackets. Without this modification, a colon within a cell array caused the rest of the code to be classified as a cell array.
Merge pull request #646 from suever/matlab_cell_flatten

Updates Matlab definition to allow colons within cell arrays