pg github: livecheck: use json api

[mascguy (Christopher Nielsen)]

Switch livecheck to use the GitHub API, as illustrated in a number of ports. (With the caveat that this example ignore alphabetic characters, to avoid pre-releases, betas, etc.)

livecheck.url       https://api.github.com/repos/${github.author}/${github.project}/tags?per_page=200
livecheck.curloptions
livecheck.regex     "\"name\": \"v([0-9\.\]+)\","

While the existing scheme works fine when checking the most recent project versions, it's limited to 10 due to pagination. Whereas the API allows us to specify how many we want, whilst also being faster.

[mascguy (Christopher Nielsen)]

p.s. We'd need to support multiple info sources, including both tags and releases. So that should be configurable.

[mascguy (Christopher Nielsen)]

Ports that currently utilize the API, are as follows:

aqua/qt5/Portfile	​https://api.github.com/repos/qt/qtwebengine/git/refs/tags
devel/icu/Portfile	​https://api.github.com/repos/unicode-org/icu/releases?per_page=100
devel/icu-devel/Portfile	​https://api.github.com/repos/unicode-org/icu/releases?per_page=100
devel/tinyobjloader/Portfile	​https://api.github.com/repos/tinyobjloader/tinyobjloader/tags?per_page=100
graphics/jasper2/Portfile	​https://api.github.com/repos/jasper-software/jasper/tags
graphics/wxWidgets-3.0/Portfile	​https://api.github.com/repos/${github.author}/${github.project}/releases
lang/libomp/Portfile	​https://api.github.com/repos/llvm/llvm-project/tags
math/sundials5/Portfile	​https://api.github.com/repos/${github.author}/${github.project}/tags?per_page=200
math/sundials6/Portfile	​https://api.github.com/repos/${github.author}/${github.project}/tags?per_page=200
multimedia/rav1e/Portfile	​https://api.github.com/repos/xiph/rav1e/releases
python/py-clang/Portfile	​https://api.github.com/repos/llvm/llvm-project/git/refs/tags
python/py-wxpython-3.0/Portfile	​https://api.github.com/repos/wxWidgets/wxPython/tags
sysutils/kubectl/Portfile	​https://api.github.com/repos/kubernetes/kubernetes/releases?per_page=100
sysutils/pwait/Portfile	​https://api.github.com/repos/${github.author}/${github.project}/commits?path=${repo_path}/${name}.c&page=1&per_page=1
textproc/hunspell-dict-uk_UA/Portfile	​https://api.github.com/repos/brown-uk/dict_uk/releases?per_page=100