xFunc 3.1.0

#148 Variable window doesn't show group name
#145 Remove duplicates of code in Argument/Left/Right properties
#144 The Equal/NotEqual statement throws NotSupportedException
#143 The 'if' statement should ignore missing 'else' part
#142 Add support of variable names with numbers
#141 Add/Sub of vector/matrix throws an exception.
#140 Review child classes of DifferentParametersExpression (constructors)
#139 Add differentiation of 'lb' function.
#138 Create Dependency Resolver to inject ISimplifier and IDifferentiator implementations
#137 Update XML documentation
#136 Rename "parameters" to "variables"
#135 Rework expressions
#134 Remove brackets from mul if parent is mul.
#133 Add simplification of negative param of mul.
#132 def/undef throws wrong exception
#130 Refactor parser, remove dependency on lexer.
#129 'if' operator doesn't work.
#128 Add support of pinch-zoom gesture to chart control
#127 Use vector text instead of icons
#126 Speed up call of 'StartsWith' method.
#125 \t, \n, \r throws an axception
#83 Laplace and Nabla-Operator