Add semantic versioning

[js6pak]

Description

Adds semantic versioning to both BepInEx and plugins.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[ghorsington]

Thanks for the PR! Here are some notes. I already mentioned some of them on Discord, here so in some cases this is a reiteration of already mentioned things.

[ghorsington]

Looks good to me

[ghorsington]

cc @bbepis for final verification on this PR

[ghorsington]

After some delibiration with Bepis, there was a new decision regarding this:

• Semver ranges are indeed needed: their immediate use is to update BepInDependency attribute to specify semver version range instead of a minimum version
  • Chainloading should be upgraded accordingly to do version range checks
• Currently used semver port to net35 doesn't have ranges while the original NuGet versioning package was too big (nor supported net35) either. Instead we should use semver.net which supports version ranges and net35 out of the box
• There is no consensus yet as to how semver.net should be included, but for now it's clear that we'll pull it directly as a NuGet package

There may be a change related maybe ILRepacking semver into core, but for now it's fine just as a NuGet package since net35 version is available directly.

[ghorsington]

Looks good to me, waiting final approval of @bbepis