Peter M. Groen / cxxopts

Fixes #143. There is no reason to make the tests optional.

Fixes #121. Removes the unused `ParseResult::get_option`.

Fixes #115. Read the version number out of `cxxopts.hpp` instead of
having to duplicate it in CMakeLists.txt.

Fixes #109. Although we always used numbers in the ASCII range, it was
in a `size_t`, leading to a warning about possible loss of data on some
compilers.

Fixes #101. Allows leading zeroes in the integer parser.

Allows unrecognised options to be left alone by the parser without throwing an exception.

This reverts commit 0f819a5cabb611ada4c41a5208c6bf1178f804be.

* Added const to argv type for better interoperability.

Fixes #102. Don't show the default value when it is a boolean and the
value is false. Note that this is a bit of a hack and the
implementation should probably be reevaluated in the future.

Fixes #93. This adds C++17 only support for `std::optional` values for
command line parameters.

Fixes #96. Default values of options not specified on the command line
had a `count` of 1. It would be better if they had a count of 0 because
they were not actually specified, so that count is only for options
given by the user.

* Add default "default" value of "false" to boolean options, therefore allowing to call result["boolOpt"].as<bool>() without throwing an exception.

* `|` should be inside of `(…)`

It's possible to use `(t|true|T|True)` as `truthy_pattern` but still failing `true` as a truthy under my environment :-(

```
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin15.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
```

Fixes #86. Rename some variables so that the overly strict shadows warning
on GCC 4.9 is not triggered.

Fixes #82. This allows the help string after the program name to be
completely replaced by the user.

Fixes #83.

Adds an overload for positional arguments taking a
`std::initializer_list`. When using an `initializer_list` with one
argument, the function call is ambiguous matching both `std::string`
and `std::vector<std::string>`.

Fixes #84. Implicit values are not handled very well. For example:

    --foo false true
    --foo --bar

In the first, `false` is an argument to `--foo`, and then `true` is a
positional argument. In the second, because of the hyphen in `--bar`, `--foo`
is parsed with its implicit value. This seems inconsistent and unintuitive.

Better is that implicit values *never* consume the next parameter to be
completely consistent. This means that values with an implicit parameter
*must* be specified using the `--option=value` form.

The parsing for boolean options was broken by 6c9bae4a07 which added implicit
and default values, and the ability to parse boolean strings. Having an option
after the boolean tried to parse that into the boolean instead of as a
positional parameter.

See #84 for the bug report.

It appears that the `libc++` available on Ubuntu 14.04 is broken and
doesn't handle the boolean regex correctly. Newer versions appear to be
correct but I have to work out how to get 14.04 to use it.

add booleans into the changelog and the readme

Fixes #54. Allow default and implicit values for booleans with multiple
boolean strings matched as values.