Swtich to 'warnings' and 'strict' pragmas

Previously, warnings and strict were turned on by mainpulating $^W and
$^H. However, the warnings pragma was introduced in perl 5.6 (March 22,
2000) and the strict pragma was introduced in perl 5.004 (May 14,
1997), fixed in perl 5.10 (December 18, 2007).

While backwards-compatibility is admirable, toast and perl are
relatively stable software, and future improvements should also lend an
eye to code readability. Using features that were introduced more than a
decade ago and are standard practice nowadays is par for the course.

In addition, since I am already requiring perl 5.6, I switched
"local($^W) = false;" to the much more robust lexical warnings
pragma ("no warnings 'exec';").
Add support for .xz files

Many programs nowadays (like GNU Emacs) are released in .xz format as
well.
Add README