Parse a string and verify it is a float.
In the above diagram:
DIGIT | → | the characters "0" thru "9" |
Ee | → | the character "E" or "e" |
EOS | → | end of string |
PERIOD | → | the period character (".") |
SIGN | → | the character "+" or "-" |
Note: The starting and ending spaces have been removed from the string.