fix `raco exe'
add "share", move "collects" back out of "lib", move "pkgs"

The "share" directory holds platform-independent files, while
"lib" holds platform-specific files.

In principle, the "collects" directory belongs in "share",
as does "doc". Those directories are put into "share"
by a Unix-style install, but left at top level for an
in-place install.

Packages in installation scope are put in "share" instead
of "lib", and the top-level Makefile puts development links
in "share/devel-pkgs".

The `configure' script now supports `--docdir' and `--collectsdir'.

Changed the version to 5.90.0.1.
distro-build: add support for source installers