Overhaul functions in scripts/set directory. * set.txi: Rewrite documentation for set functions. * intersect.m: Rewrite docstring. Use by_rows variable for code clarity. Return output orientation which is compatible with Matlab. Add %!tests for output orientation and N-dimensional inputs. * setdiff.m: Rewrite docstring. Use by_rows variable for code clarity. Rename output i to ia to clarify it is an index into the set a. Return output orientation which is compatible with Matlab. Add %!tests for N-dimensional inputs. * setxor.m: Rewrite docstring. Use by_rows variable for code clarity. Return output orientation which is compatible with Matlab. Add %!tests for output orientation and N-dimensional inputs. * union.m: Rewrite docstring. Use by_rows variable for code clarity. Return output orientation which is compatible with Matlab. Add %!tests for output orientation and N-dimensional inputs. Add %!tests for validsetargs which are common to all set functions. * unique.m: Rewrite docstring. Verify that input is numeric or cell array of strings. Avoid computing idx for optional i,j outputs unless required. Add %!error tests for input validation. * ismember.m: Rewrite docstring. Use input variable 'a' instead of 'A' for conformance with rest of set functions. Rename output index variable to s_idx for clarity that it is an index into the set s. * powerset.m: Rewrite doctring. Add input validation on nargin. Add %!error input validation tests. * module.mk: Include validsetargs.m in build system. * validsetargs.m: Function renamed from validargs which was too general. * validargs.m: Function renamed to validsetargs.