Bump $VERSION to 1.06 and properly set it to avoid warning.

$ perl -w -mversion -e '$VERSION = substr q$Revision: 1.05 $, 10; version->parse($VERSION);'
Version string '1.05 ' contains invalid data; ignoring: ' ' at -e line 1.

http://perldoc.perl.org/perlmodstyle.html#Version-numbering
Makefile.PL: set ABSTRACT, AUTHOR, LICENSE and MIN_PERL_VERSION.

So that the generated META.yml has more information, pass ABSTRACT,
AUTHOR, LICENSE and MIN_PERL_VERSION to WriteMakefile().
Makefile.PL: add postamble for new 'mydist' target.

The 'mydist' target builds generates a SIGNATURE and includes it in a
generated tarball.  Inspired by libnet. [1]

[1] http://cpansearch.perl.org/src/GBARR/libnet-1.22/Makefile.PL
Prep for 1.06 release: update CHANGES and README.