Create ContextManager and it works as expected
Split ExpressionContext Class from Context Class
Modify on Context, ExpressionContext and FlowControlContext
so that they works properly with Context Manger

Add tests for FlowControl operator 'while' without '{' and '}' operators
Modify test fixture for Expression Context
Last push to merge

some minor changes on Lexer.py and its test code
Last push for merging
Merged with the latest.