Fix : 1 pound = 453.59237gm

1 pound = 453.59237gm.

Initially, it was "1 pound = 16gm".

also fixed a unit case issue, make sure to be consistent everywhere, also made sure
that if the same abbreviation is used across unit groups that the conversion can
find them

also updated the examples, updated README, added 'getUnitType' function

units.convert now accepts a string for conversion rather than parameters,
the unit types are now determined rather than needed to be given,
the plurarl forms of units are now accepted,
numerizer was added to accept values such as 'forty two',
fixed some incorrect units in default unit db,
update README, added some simple examples