Some updates in function docs
Implemented support for `null` in all functions (see #205)
Fixed #205: A returned matrix subset is now only squeezed when the `index` consists of scalar values, and no longer for ranges resolving into a single value.
Added test to test for numerical issues just fixed
Changed calculation of math.sqrt to avoid numerical problems when re < 0
Merge pull request #208 from pavpanchekha/develop

Numerical imprecision in complex square root
Fixed a broken link
Implemented function `flatten`
Changed the default value of new entries in resized matrices to zero.
Merge remote-tracking branch 'origin/develop' into develop
Updated docs
Implemented function `sort`
Some refactoring of the FunctionNode
Implemented support for raw functions
Raw functions are now invoked as fn(args, math, scope)
renamed `__transform__` to `transform`
Changed default value of the option `wrap` of function `math.import` to false, and fixed a but in math.import
Updated docs
Documented function transforms and custom argument parsing
Expressions in the expression parser can now be spread over multiple lines