Test for either asterisks or underscores

Pod::Markdown has switched to double asterisks for bold formatting, and
the tests previously only accepted double underscores, resulting in a
failure. This now test for either asterisks or underscores for both bold
and italic, so the tests should pass regardless of what Pod::Markdown
decides to do in the future.

Fixes #13. See also https://github.com/rwstauner/Pod-Markdown/pull/10
Acknowledge ETHER's contributions in module's POD
v0.141120

    - Adjust tests for change in Pod::Markdown output
Load Pod::Simple::{HTML,Text} dynamically
Delay loading of PPI::Document

Delay loading of PPI::Document. This will help to speed-up `dzil
listdeps` (unless other plugins require it).
Explicit loading of PPI::Token::Pod is removed: if POD elements are
found in the file, the package will have been loaded by PPI::Document.
And if there is no POD element, we will never use that package.
Document how to put the same readme in both locations

Fixes #3.
Replace implicit Path::Class use with Path::Tiny

The code in "t/rootprune.t" implicitly required a higher version of
Path::Class than Dizt::Zilla itself does, but this module doesn't
specify a higher version requirement. This is fixed by using Path::Tiny
instead, since Path::Tiny is already being used elsewhere in the module
anyway.
v0.141760

    - Load some modules dynamically only when they are used
    - Eliminate implicit dependency on specific version of Path::Class
    - Minor documentation updates