Fix memory leak, closes #190
Fix unused variable warning
Replace `rm_const_and_ref` with `std::decay`
Fix operator== for invalid optionals, close #191
Simply implementation of `to_guard`
Use inline functions for trait constants

Visual Studio struggles with `constexpr float` static members. We work around
this issue by using inline functions instead.
Fix macro check for non-GCC, non-Clang compilers
Remove unused template parameter pack
Remove constexpr around empty (inline) function
Remove constexpr for `mapped_int_name` getter
Add explicit constexpr ctor where possible
No install targets on WIN32 and no compiler check
Make `check_typed_input` non-constexpr
Remove `discard_behavior`
No more constexpr lookup table for atoms
Use struct for `get_wildcard_position`
Use less general implementation for `tl_back`
Add constexpr ctor to `arg_match_t`
Add constexpr ctor to `detail::wrapped`
Work around ridiculous VS compiler bugs