Variadic additions and recode

Simplified message framework internal code.
Additional receive() virtual function overload taking destination id.
Removed is_bus() member function.

Added variadic template versions of etl::largest, etl::largest_type,
etl::largest_alignment and etl::smallest

Bug fix for 'vector of pointers'

Fixed bug in 'vector of pointers' move constructor

Added 'delegates'

Added a C++11 compatible etl::delegate template class.
Improves and extends the functionality offered by etl::function.
Added etl::delegate_service to complement etl::callback_service

See https://www.etlcpp.com/delegate.html

Secure Strings

Added missing 'cleanup' to string's resize() method.

Secure Strings

Added an optional secure mode to strings, so that unused space will be cleared to zero
They are also cleared on destruction.

multi_array, memory_clear, memory_set

Added etl::memory_clear and etl::memory_set utility functions.
These functions will overwrite the memory allocated to the supplied object, or pointer and range.

Added variadic min and max functions.
etl::multimin
etl::multimin_compare
etl::multimin_iter
etl::multimin_iter_compare
etl::multimax
etl::multimax_compare
etl::multimax_iter
etl::multimax_iter_compare
C++11 only.

Added etl::multi_array

Added a C++11 or above multi-dimensional array template.

Fixed unsigned cyclic_value wrap-around bug for negative advance.

Calling advance on an unsigned cyclic_value with a negative step, that would cause the value to wrap around the lower bound, would result in the incorrect value.

Fixed bug in to_string for floating point with leading zeros after the decimal point.

Fixed bug in fractional part for floating point with leading zeros after the decimal point.

Added 'to_string' functionality

Added 'to_string' functionality for integrals, floating point, bools and pointers.
Added etl::format_spec classes to describe the require string formatting.