Replace boost::regex with std::regex

Issue/feature addressed

This MR replaces boost::regex with std::regex.

Proposed solution

This is essentially a drop-in replacement, although boost::cmatch has also been replaced with std::smatch in a few places to be a bit more modern and avoid need to call .c_str().

Implementation

Note that std::regex is really a C++11 extension, but this was a bit poorly implemented in some compilers. Since initial attempts to replace were several years ago, the regex libraries are now sufficiently mature to apply this now.

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

Please add any other information that could be useful for reviewers.

Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).