Peter M. Groen / cxxopts

Uses std::exit instead of abort to terminate when exceptions are disabled.

Fixes #219. The example was wrong as ParseResult can't be returned out
of scope of the options parser.

Fixes #201. Parse char type correctly and check for length.

Fixes #202.

Fix CXXOPTS_NO_EXCEPTIONS so that it doesn't warn about unused parameters, and print out error messages.

Fixes #197. Don't parse default options twice when there is a short and
long option.

Install targets will not be generated if this option is set to OFF,
which is useful when including it as a bundled dependency of
another project.

This speeds up the CMake configuration step by not searching for a C
compiler. By default, CMake looks for C and C++ compilers, unless a set
of compilation languages is specified.

Allow adding options with a single initializer list.

Some positional parameters would be listed in the help text and others
would not, when what is desired is that no positional parameters are
listed with the other command options. This change suppresses the help
listing for all positional parameters.

Improve parsing into std::vector so that a single argument can take a list.

These were detected using -fsanitize=undefined parsing values equal to
INT_MAX and INT_MIN.

* Parse 1 as "true" and 0 as "false" for boolean options.

Fixes #171. Allows invalid syntax for short options to be ignored.

Fixes #175. This was broken when throwing an exception on missing
positional parameters in #169.

Fixes #169. It seems reasonable to throw an exception when an attempt is
made to parse into positional parameters that don't exist.

String literals with the prefix `u8` now have the type `const char8_t[N]` in
C++20. As a consequence the library does not compile in c++2a mode with GCC
(you can't concatenate `std::basic_string<char>` and `const char8_t[]` as
`char` and `char8_t` are different types).

Fixes #166.

The empty string caused the vector to have one element which caused
the test at line 2041 to always fail.

Fixes #157. Fix the wording in the README about booleans.