Add Linux and macOS support :)

This version adds support for Linux x64 and macOS x64. In all other aspects, it's the same as v0.8.0.

Target .NET Standard 2.0

This is a major rewrite:

• The library now targets netstandard2.0 - it works on the .NET Framework and on .NET Core on Windows.
• No more C++/CLI, so no more dependency on the VC++ redistributable.
• The library is now exclusively shipped as a NuGet package, the native code is no longer embedded into the managed assembly.

• Update to PCRE v10.32

Update to PCRE v10.31

• New flags in PcreOptions: ExtendedMore, Literal, EndAnchored
• Added a pattern conversion feature through the PcreConvert class: convert POSIX BRE, POSIX ERE and glob patterns to PCRE
• Added support for custom JIT stacks through PcreMatchSettings.JitStack
• Added new flags to PcreCallout: StartMatch and Backtrack
• Added PcreNewLine.Nul
• Added PcreRegexSettings.ExtraCompileOptions
• Renamed RecursionLimit to DepthLimit
• Added more information to PcrePatternInfo and PcreBuildInfo
• Rewrote the build script using Cake, and fixed some build issues along the way

Update to PCRE v10.23

• Update to PCRE v10.22
• New flags: PCRE2_ALT_VERBNAMES, PCRE2_USE_OFFSET_LIMIT, PCRE2_NO_JIT
• New info: PCRE2_INFO_HASBACKSLASHC
• Add support for pcre2_set_offset_limit, pcre2_set_max_pattern_length

• Update to PCRE v10.20
• Requires the Visual C++ 2015 redistributable
• String-based callout support (e.g. foo(?C{hello})bar)
• New flags: PCRE2_NEVER_BACKSLASH_C, PCRE2_ALT_CIRCUMFLEX

• Update to PCRE v10.10
• DFA matching
• UTF validity check on by default

Updated to PCRE version 10.00 (aka PCRE2).

The public API has been refactored to account for the PCRE API changes.

New: Partial matching and single match options.

Breaking change: PcreRegex.Match will return a PcrePossibleMatch object on failure, with an IsMatch property set to false.
This is necessary for partial matching support and is consistent with .NET's Regex.Match behavior.

• Last mark is returned in match result: (*MARK:foo) -> match.Mark == "foo"
• Callout support ((?C1)) through a callback:

var regex = new PcreRegex(@"(\d+)(*SKIP)(?C1):\s*(\w+)");

var match = regex.Match(
    "1542: not_this, 1764: hello",
    data => data.Number == 1
            && int.Parse(data.Match[1].Value) % 42 == 0
                ? PcreCalloutResult.Pass
                : PcreCalloutResult.Fail);

// => match[2].Value == "hello"

Initial PCRE.NET release