updating Plugin.simple_extract docstring
Add string normalisation to the base plugin class.

simple_extract() in the base plugin class now:
1/ strips the HTML tags
2/ strips all characters except the latin letters and digits + the ' '
blank space character, ASCII 0x20
3/ normalises all remaining whitespace, replacing multiple whitespace
characters with the ' ' blank space char
4/ lowercases the string

These operations are applied to both the incoming page source and the
license statement which we're looking for in that page's source.
put in some commented out logging statements in base plugin class
do not strip html/special chars by default in simple string matching, causes subtle problems e.g. Hindawi
minor fixes to plugins
fix second tutorial example test, was purely imaginary data which caused it to always fail