v1.3.0 release

This release contains several fixes and improvements.
Note: API's are backward compatible with previous release.

Fixes

#71 fix dummydefine for mbed_trace_init
#65 Ensure tr_array doesn't print when len == 0
#52 Use temp variable in mutex release loop
#51 Fix race condition when unlocking mutex
#40 Changed dummy definitions to match the actual functions' return types
#39 FEA_TRACE_SUPPORT flag is always set when traces are enabled.
#45 Fix disabling traces through the YOTTA_CFG_MBED_TRACE flag.

Improvements

#66 output/ added to gitignore list
#63 Added include_directories(${CMAKE_CURRENT_SOURCE_DIR}/) include to re…
#61 Add CMakeLists.txt to support PAL Tools
#58 Fix header documentation
#57 Update README.md
#54 Provide environment-agnostic configuration macros.
#53 Flash size can be limited by defining MBED_TRACE_MAX_LEVEL
#50 Add instructions for enabling the library in mbed OS 5
#47 Editorial changes.
#46 Allow setting mutex locking/unlocking callbacks before trace init.
#44 Ipv6 helpers update
#43 Deprecate the misnamed YOTTA_CFG_MTRACE_TMP_LINE_LENGTH flag.
#68 Release v1.2.2 (there is no tag for this, was "hidden release")