Protect fieldmapCache with an RWMutex
Merge pull request #31 from kisielk/rwmutex

Protect fieldmapCache with an RWMutex
allow embedded struct pointers to work as regular embedded structs do, fixes #35
factor out the code which converts a nested struct mess into a well ordered list of field reflect.Values so it can be reused in NamedQuery, fixes #24
Simplify some reflection code.