Add BoundValue Implementation

[jeffgbutler]

Bound Values are rendered into SQL as bind parameter markers only, and their values are added to a parameter map.

This is useful when coding a function like the following:

  UpdateStatementProvider updateStatement = update(person)
    .set(age).equalTo(add(age, value(1)))  // value() function added in this PR
    .where(id, isEqualTo(5))
    .build()
    .render(RenderingStrategies.MYBATIS3);

Inspired by #737

[coveralls]

coverage: 100.0%. remained the same
when pulling 3592b30 on jeffgbutler:gh737
into 1dcdbfd on mybatis:master.