Vector and Visitor updates

C++11 variadic templates for visitor pattern classes etl::visitable and etl::visitor
Added external buffer support for etl::vector

Extended use of truncate flag in strings.

Strings can inherit the truncation state if constructed or modified in some way from a string that has its truncate flag set.

Fixed operation 'truncated()' for strings.

'truncated()' did not accurately indicate the truncation state of the string in all circumstances.

Bug fix, updates and new spsc queue

Fixed string push_back() bug where there internal terminator was not updated.
Basic Conan package added.
Added const ref istring constructors.
Added queue_spsc_locked with injected lock and unlock functionality.
Updated profiles for C++17.
Enabled emplace functions for C++03.
Move C++03 force macros to profile.

Fix inconsistent ETL_FILE definitions

Fix inconsistent ETL_FILE definitions

Bug fixes + rvalue references for forward_list

Fix 'force C++03' macros leftover from testing.
Added rvalue reference interfaces to forward_list.
Fix for unordered_multimap, unordered_set and unordered_multiset insert and erase bug.
Fix for unordered_map insert and erase bug.

C++11 macros and std::forward

Added ETL_NOEXCEPT macros.
Added std::forward support to alternate STL utility header.

New features, updates and fixes

Added #include to message_router.h for improved cross platform compatibility.

Added etl::callback_service
Useful for abstracting the interrupt system from C++ handlers.

Fixed bug for certain inserts in etl::vector

Added missing #include "stl/interator.h" in frame_check_sequence.h

Added constexpr constructors to string_view and array_view.

rvalue reference API for deque, list & vector + others + fixes

rvalue reference API for deque, list & vector.
etl::scaled_rounding
etl::cumulative_moving average
Fix to etl::flat_map [] operator & insert.

Fixed compile error pushing literals to etl::deque

Rvalue reference overloads were incompatible with the internal parameter_t type when pushing fundamental type literals.