Allow for parsing exactness and radix flags
fixed to support appropriate digits
throw an error instead of returning false

Emmanuel asked for the fromString function to throw errors instead of returning
false.
add some comments regarding unreachable cases
only throw errors when a string _must_ have been a number

a string that doesn't start with a reader macro (i.e. a hash modifier) could be
a symbol instead so return false and the parser will try to read a symbol or
identifier.
fix hashModifiersRegexp s.t. it only matches when there is a hash modifier

The previous implementation had the weird behavior that the variable hMatch
wasn't `null' when there were no hash modifiers, which seems counter to its
name. This confusion resulted in the introduction of a bug via the last
commit. This bug is resolved by this commit.
Merge pull request #1 from danking/master

Add functionality for parsing number exactness and radix hash-modifiers