pkgtools/cabal2pkg: import cabal2pkg-0.1.0.1

cabal2pkg is a tool to automate importing Haskell packages to pkgsrc and
updating existing Haskell packages in pkgsrc. cabal2pkg is similar
to url2pkg(8), in that it downloads a distfile, extracts it, and generates
package Makefile and other files, but it is specialised in Haskell packages and
is intended to generate mostly complete Makefile.

cabal2pkg can also update existing packages by performing 3-way merge on files.
In the update mode, cabal2pkg fetches two package metadata of the current and
the updated version, then tries to apply differences between two versions
against the current set of files.