buildPerlModule: Call "./Build build"

Some modules require this.
Consistent whitespace
Rewrite the CPAN generator to Perl

Also:

- It's now installable by doing "nix-env -i nix-generate-from-cpan".

- It maps dependencies to the correct attribute (e.g. HTML::HeadParser
  is mapped to HTMLParser).

- It automatically selects buildPerlPackage or buildPerlModule.

- It's documented in the manual.
Update some Perl packages