Updated version number to 0.8.3-SNAPSHOT
Use polynomial-time algorithm to compute determinant.
Merge pull request #12 from bcuccioli/master

Compute determinant in polynomial-time.
Some comments updated
Strongly simplified Scope (Workspace not yet working with simplified scope)
Removed redundant prototype math.expr.Symbol
Splitted AssignmentNode in AssignmentNode and UpdateNode
simplified Workspace and Expression, works now with the strongly simplified Scope
Moved RootScope to a separate file
Comments updated
Implemented function math.parse(expr [,scope]), extended function math.expr(expr [,scope]).
Updated documentation on eval, parse, and parser
Some more tests added
Implemented cache in Scope
Removed RootScope
Implemented function subset, including support for string and scalar
Added an example file extend.js, updated readme
Implemented context variable `end` for subsets of strings
Fixed in mod for negative numerators. Added more input validation. Added tests
Implemented construction function number