fix coverage upload (without release)

reference FParsec 2.0.0-beta

target netstandard2.0 for net481 support

upgrade dependency FSharp.Core

🐛 fix implementations of `Many1Strings(p, sep)`

declare nullability correctly for Opt() and when unwrapping parser replies +semver:skip

install cake tool before build

declare nullability correctly for Opt() and when unwrapping parser replies +semver:skip

update cake and nuget api key +semver:skip

ignore coverage report +semver:skip

wip: udpate cake +semver:skip

wip: udpate cake +semver:skip

update deps +semver:patch

set project url correctly +semver:patch

declare nullability correctly for Opt() and when unwrapping parser replies +semver:patch