This fixes issue #47 and simplifies the CamelCase regex

The simplified regex allows the following migration class names:
CamelCase -> camel_case
Camel34 -> camel34
CamelCase23afterSomeBooze -> camel_case23after_some_booze

It does NOT allow (which was previously allowed):
CAmelCase

The mail reason for not allowing consecutive uppercase letters is because something like this:
SOMETHING
gets transformed to:
s_o_m_e_t_h_i_n_g
and i don't really see why anyone would use that other than forgetting the caps lock on by mistake (in which case we'd better warn him)