Boolean tokens, 'in' and 'divby' operators, 'geo.intersects' operator, 'IN' operator

[sebastien-rosset]

The 'in' and 'divby' operators are now supported by the OData spec. See http://docs.oasis-open.org/odata/odata/v4.01/csprd02/part1-protocol/odata-v4.01-csprd02-part1-protocol.html#_Toc486263411.

• Add support for boolean tokens (true, false)
• Add support for the 'in' operator. For example, it is possible to parse the following ODATA query filter:
  Name eq 'Bob' and contains(LastName, 'Smith') and City in ('Dallas', 'Houston')
  The 'IN' operator uses open and close parenthesis as a delimiter for multi-value operands. Previously, the parenthesis were used as a delimiter for operator precedence.
  http://docs.oasis-open.org/odata/new-in-odata/v4.01/cn02/new-in-odata-v4.01-cn02.html#_Toc495652512
• Run gofmt, fix some space formatting issues
• Add some code comments.
• Fix typo for the 'geo.intersects' operator
• Add 'divby' operator. The new divby operator promotes both operands to decimals and always results in a decimal. http://docs.oasis-open.org/odata/new-in-odata/v4.01/cn02/new-in-odata-v4.01-cn02.html#_Toc495652513
• Fix precedence order between 'or' operator and lambda operator
• Fix crash when query includes operator or function that does not have enough operands
• Add positive and negative unit tests
• Add substringof function
• “substring” function was incorrectly parsed as “sub” operator
• "substring" function can take 2 or 3 arguments
• Support for variable number of function arguments.
• “isof” was incorrectly parsed as operator. It is a function.
• "length" function was incorrectly parsed as "le" operator.
• "indexof" function was incorrectly parsed as "in" operator.
• Add UTs for filters provided as examples in the ODATA spec.
• Support isof function with one or two arguments.
• Add support for '@' character, which is used for parameter aliasing