Fixed adding to Formats an upcasted FieldSerializer[Any].

Fixes #74
Skip reflecting static *and* transient fields.

This fixes a stack overflow for at least singleton objects and
AtomicInteger when a FieldSerializer is present.

Scala objects have a static self-reference MODULE$ field and
AtomicInteger has a static pointer to sun.misc.Unsafe,
which in turn has a self-reference.

Related to #74 (can easily trigger this problem).
Merge pull request #75 from mpartel/issue-74

Fixes for #74