Fix CMake find_package for Conan build

v2.1.5

Remove CMake fmt find_package option (#50)

Bug fixes

• Fixed bug triggered when replacing console interfaces.
• Fixed race condition issues.

Build system and dependency fixes

• Updated some dependencies.
• Fixed some CI build system issues.

Minor CMake fixes

• Fixed a minor issue with naming in CMake.

CMake fixes

• Made important CMake changes required for properly making Conan packages. (ed-alertedh)
• Made minor changes to the code to prevent issues when using a using namespace std; statement.
• Minor documentation changes.

CMake fixes

Changes

• Fixed faulty CMake code that did not properly import dependencies.

Important new features and performance improvements

New features

• Added flushing functionality, see documentation for details in how it works.
• Added support for the fmtlib (for formatting) if present.
• Significant performance improvements. This library is now (in many simple cases) significantly faster than spdlog.

Other changes

• Added performance tests.
• Replaced the home-brewed concurrent queue with a much faster open source one.
• Made the logger run in a separate thread.
• Improved/fixed the README-file.
• Made it easier/possible to build the library without using Conan for providing dependencies.
• Added and fixed examples.
• Fixed the non-working emptyQueue() and queueSize() implementations.
• Fixed/improved code documentation.
• Removed the message queue size parameter from log message handlers as it was deemed unnecessary.
• Fixed and added unit tests.

Note that this release has not yet been extensively tested in a production environment. This will be done starting from today (2020-01-20).

Fix of severe build issue and other minor improvements

• Fixed a bug that prevented the library from being included as a conan package in other projects.
• Moved some of the code from externally facing header files to internal header files. This reduces the number of includes.
• Other minor CMake and code fixes.

Updated JSON for Modern C++

Updated the JSON for Modern C++ from 3.1.0 to 3.6.1.

Update ASIO dependency

ASIO has been updated from 1.12.0 to 1.13.0.