Every modern hardware, including embedded devices, should support floating point numbers.

It was not fully implemented and such feature should be implemented in separate module or on developers own.

This is a new memory subsystem implementing heap calculations as well as new builtin functions:
 * get_memory_usage()
 * get_memory_peak_usage()
 * get_memory_limit()
It also allows to set an upper memory limit, ensuring that processed script will not be able to allocate more memory from OS.
New subsystem is based on work done in 'memory_limit' branch. Big thanks to devnexen!
This finally fixes #25.

First of all, VFS is not a right place for this, finally it was not implemented anyway.

* some functions were not used and have been removed
 * some parameters seemed to be useless and have been removed
 * code cleanup