0.0.7

This release introduces a new way of installing ghcup (and GHC and cabal in the process)
with the infamous curl .. | sh pattern. See #36 for discussion. This
is completely optional.

Features:

• Add a bootstrap-haskell script, fixes #36
• Allow to specify tags for ghcup install, ghcup install-cabal and ghcup set
• ghcup list also shows tags
• support installing on macOS aka Darwin
• Improve detection logic for CentOS/Alpine/AIX/FreeBSD
• Introduce a GHCUP_INSTALL_BASE_PREFIX env variable to control where .ghcup directory will be created
• Add rudimentary support for Amazon Linux

Bugfixes:

• Create missing haddock -> haddock-ghc symlink
• Emit distro-alias inferred in debug-info output
• Tweak exit code for ghcup install (If a GHC is already installed, we shouldn't treat it as an error)

Cleanups:

• Simplify mkdir calls
• Documentation improvements
• Error handling improvements

API changes:

• self-update was renamed to upgrade