Many improvements. Candidate for 1.1.0

- Added the Hexdump class to set global options
- Added HTML output
- Added stderr output
- Added direct output (instead of returnin the dump)
- Added test suite

- Deleted the obsoleted demo.php
Updated and enhanced README.md for github
Fixed phphd according to new Hexdump.php

- Fixed the hexdump() call as its signature has changed
- Introduced -f (format) param
- Minor refactoring (removed useless code)

- Updated the usage of phphd in the README.md