support the method overload

[xiaoma20082008]

add new configuration to support the java's method overload

[harawata]

Thank you for the PR, @xiaoma20082008 !

Most users who requested overloaded methods seemed to want to map multiple overloaded methods to a single XML statement (e.g. #705 ).
For example, mapping the following two methods...

User findUser(Integer id);
User findUser(Integer id, String name);

...to this XML statement.

<select id="findUser" resultType="User">
  select from users where id = #{id}
  <if test="name != null">
    and name = #{name}
  </if>
</select>

It is already possible with Java 8's default methods.

default User findUser(Integer id) {
  return findUser(id, null);
}
User findUser(Integer id, String name);

This PR, however, maps a different XML statement for each overloaded method.
Is this really what you want?
Isn't it better to name these methods differently in such case?

[xiaoma20082008]

Thanks for your replying @harawata .
Because of some developers in my company use this future under jdk7, so I developed this patch also I'm pushing them to use a different method name but it's slowly.
If most users don't need this patch, Please close this pr ,Thank you!

[harawata]

Thanks for the explanation, @xiaoma20082008 !

So, it is a kind of special case and not many users are in the same situation, I guess.
I'll close this PR for now, but will keep watching requests.

Thanks again for taking the time to submit the PR!

Note to self:
In case we support overloaded methods in the future, this approach (auto-generating statement ID from method name and parameter types) makes IDs too verbose, in my opinion.
It might be better to let users assign a new statement ID explicitly via some annotation (e.g. @StatementId("newName")).