Bug fixes & enhancements

matlib 0.9.8

• added circle() for drawing circles in diagrams
• vectors() now handles 0-length vectors more gracefully #50.
• matrix2latex() generalized to allow different bracket types and optionally show the size of the matrix.

matlib 0.9.7

• inv() and aliases now return invisible matrix when verbose = TRUE to match behaviour of related functions (e.g., gaussianElimination())
• GramSchmidt() gains an argument, omit_zero_columns to control whether all-zero columns are retained in the output (issue #48) [Thx: @ggrothendieck]
• Merge pull request #49 from JF to retain column names in GramSchmidt().