Add config file.

Adds testing of existance for various headers in `CMakeLists.txt` and
simple config file.
Add exact sized integer type definitions.
Switch to 64 bit integers in Value class.

Use 64 bit integers in `Value` class and also remove the useless
`m_data.b`.
Add number to string conversion methods.
Add value conversion methods.

Adds methods which can be used for converting `Value` objects into
numbers.
Bug fix: Method call arguments.
Add number API.

Adds number classes and operators.
Add attribute inheritance for classes.
Merge pull request #5 from peelonet/64-bit-integers

64 bit integers