Minor changes and fixes. Fix for GCC atomic.

Minor updates for etl::delegate
Fixed incorrect results returned from pointers for atomic_gcc_sync
Added #include "stl/utility.h" to etl::optional
Added const parameters and ETL_CONST_EXPR to etl::array_view
Removed redundant etl::const_array_view

Various small fixes

void assign(const_pointer, size_t) did not set the truncation flag.

Fixed resize(0) error for etl::forward_list

Removed erroneous pointers in etl::unordered_map::begin()

Optimisation of etl::cumulative_moving_average.

Optimisation of floating point specialisations of etl::cumulative_moving_average.

Runtime sample size specialisations to etl::cumulative_moving_average

Added specialisations to etl::cumulative_moving_average where the sample size may be set at runtime.

Fixed compile error with C++17

Removed ETL_IF_CONSTEXPR from etl::message_timer 'tick()'

ETL's random number generators are now non-polymorphic by default.

ETL's random number generators are now non-polymorphic by default.
Define ETL_POLYMORPHIC_RANDOM to enable previous functionality.

Moved global operators to ETL namespace

Moved global operators to ETL namespace.

Small additions and fixes

A few small optimisations to binary.h
Added variadic parameters to etl::observer notification
Fixed misplaced semicolon in error_handler.h
FSM test example fix
Compatibility changes for GCC v5.4

Added #include <new> to files using 'placement new'.

Added #include to files using 'placement new'. Fixes missing definition that can sometimes occur.

Simplified 'to_string' templates

Simplified 'to_string' templates.
Changed parameters from etl::string to etl::istring.
Same with other 'to_string' variants.