v1.0.0-rc.3

Another release candidate. A few more breaking changes, though less
drastic than rc.2 was. Things are slowly stabilising.

Thanks to @Duncaen for his contribution to this release.

Breaking changes

• core.Pi.Range has been renamed to core.Pi.Codomain (#12)
• core.TextLit has been removed and replaced with core.PlainTextLit.
  There is no longer a (public) interpolated text Value type.
• struct tags are now dhall not json (#15)

Fixed

• fixed a parser bug related to single quote strings (#1)

Changed

• faster parser by approx 30% (#11)