Build system and packaging maintenance

• Adjusted CMake to only look for Catch2 if tests are being built. Reduces warnings for projects which use something else (e.g. GTest)
• Change building instructions to work with conan 2.0 CMakeDeps generator - This sets the minimum CMake version to 3.23
• Remove conan recipe as it is maintained in the conan center index

`as()` automatically infers underlying type

• Bugfix: unit.as<other_unit>() automatically infers the underlying type if not explicitely specified.
• Using Catch2 test discovery in CMake

Proper spacing in string conversions and correcting spelling mistakes

• Removed implicit conversion from primitives to unit_t. See issue #106 for details
• When converting units to string a space is inserted between the value and the unit, as described in the SI brochure, section 5.4.2

  • The numerical value always precedes the unit and a space is always used to separate the
    unit from the number

• Fix various spelling errors (thanks to melg8).
• Renamed sterradiant_t to steradian_t which is correct

Bugfix and more convenient conversion function

• Fix reported issue that operator/(scalar / unit) would calculate the ratio into the value.
• Add function as<unit_t>() to unit for convenient conversion to a unit of the same type but different ratio
• CMake Linting

Flow units

• Add surface flow and volumetric flow units

String conversions for velocity and acceleration

• Add string conversions for velocity (m/s) and acceleration types (m/s^2)

Add degrees to angle type

• Add degree_t to angle type including literals _deg - Conversion between radians and degrees are possible

Add type conversion for cross-unit operations

• Fix CI pipeline for windows
• Add missing conversion between float and double for operator/ and operator* for operations between different units

Update dependency to catch to 2.13.6

• Update to catch 2.13.6 in the conan recipes
• Remove deployment to bintray.com as it is scheduled to sunset on May 1 2021
• fix recording of benchmarks

Conan no longer mandatory for tests

• Tests are built without the need for conan if catch2 is found. (using conan is still the preferred way) fixes #90
• Cleaning up obsolete todos and typos