Update Swift CI Versions to 5.1.5 and 5.2

Updates the CI so that the official version of Swift is 5.1.5, while also building 5.2 in planning for later migration.

Make it Possible to Re-Bootstrap

Merge pull request #64 from Kaiede/vNext

Prep 1.0 for Release

Update To Swift 4.1.3 and 4.2 on Linux CI (#59)

Add Test for 32-bit Overflow

Swift 3 Doesn’t Have DispatchTimeInterval.never

This broke tests further…

"./install.sh update" should use tags

Instead of always syncing to the head, this command should sync to the latest tag. This will make it a bit easier to merge work back into master without exposing it to users as a byproduct.

Make Mac Travis Build Faster

Telling Travis that it is swift makes it take about 4 times as long as it pokes things like the iOS simulator we don’t care about. We just need the ‘swift’ command which is already in the Xcode images.

Talk about Per Channel Tweaks in README

Fix Installer

The command to unpack the swift tarball didn't actually do the unpack.