add number tests

[pjfanning]

• relates to conversation starting at [json-org] fix issue with parsing big numbers #32 (comment)
• the number behaviour changed in v2.15.0
• both jsr-353 and json-org provide getters on their Json Value APIs that allow users to choose what number format they want - users have this control
• users who insist on using the APIs that return java.lang.Number will see differences after v2.15. They get a BigDecimal instead of a double. This is a little unfortunate but the changes help users who need us to retain the precision of big numbers.
• I would prefer not to make big changes and not to revert the 2.15 changes. I think it is better to play it by ear - to see just how many people complain and get their reasons why they can't make small changes to their own code to react to the jackson change.

[cowtowncoder]

Obsoleted by #40, closing.