Fixed Mojo::URL regression

Mojolicious have changed the way Mojo::URL parses
URLs since 3.97. Instead of relying on Mojo::URL we
parse the URL by ourself.

Added testcases for new URL parser.
Removed the 508byte block limit

Instead of hardcoding the block limit to a value,
which also breaks the RFC, let the limit be dynamic.
This will open up for support of RFC2348 (block > 512byte)
at a later time.
Released version 0.02

       * Fixed Mojo::URL regression
       * Fixed 508 byte block RFC-violation
         Author: https://github.com/hemmop
         https://github.com/jhthorsen/mojo-tftpd/pull/1