remove outdated documentation of caveats

- only EUMM should be used for dual-life modules
- other MakeMaker plugins *should* work (tests forthcoming), or patches will
  be immediately applied to make them work
prefer List::Util, which is in core
some modest tests to ensure the content was added to Makefile.PL
add irc channel and mailing list info to metadata
head header to Changes, and canonicalize timestamps
shorten this pod directive
switch to my plugin bundle
tighten up entries
add clean namespace test
do nothing if entered_core is sufficiently high
extract entered_core from Module::CoreList (based on patch from leont)
do not permit use with non-dual-life (actually, non-core) modules
Dist-Zilla-Plugin-DualLife-0.04

          - do nothing if the version the module entered core is late enough
            that no special action is needed
          - calculate 'entered_core' parameter from Module::CoreList, rather
            than assuming 5.009005
          - build fails if module is not dual-life at all