Added basic checker for duplicate attributes.
Removed duplicate @property attribute.
Added more attributes to the duplicate checker.
Added pure and nothrow to the duplicate attribute checker.
Merge pull request #176 from workhorsy/duplicate_attribute

Duplicate attribute checker
Fix AST output for several tokens
Prevent false positive in slice error
Use binary literals for bit masks
Move string interning out of std.lexer
Fix issues with doc comments being missing from some declarations
Support parsing of virtual functions
Fix incorrect unused parameter warnings in function types
Update lexer and parser for 2.066 language changes
Issue warning on LastCatch as well
Fixed issue where warnings on line zero would break unit tests.