A Term represents a word from text. This is the unit of search. It is
composed of two elements, the text of the word, as a string, and the name of
the field that the text occurred in, an interned string.
Note that terms may represent more than words from text fields, but also
things like dates, email addresses, urls, etc.
Compares two terms, returning a negative integer if this
term belongs before the argument, zero if this term is equal to the
argument, and a positive integer if this term belongs after the argument.
The ordering of terms is first by field, then by text.