get rid of redundant ALLOWED_PROPERTY_TYPES
remove basestring from MAP_TYPES_PROPERTIES

test that the reason it was added does not break
make the treatment of types completely configurable

- reverts/replaces the recent "_string_conversions" addition to the api
- adds a 'Meta' class to the JsonObject api, for configuring this kind
  of setting
- move "convert" file's parts into other files
add and test update_properties Meta variable
remove support for python 2.6
allow unknown options in Meta

this is to allow, for example, couchdbkit to highjack this as well
bump version to 0.6.0
r-prefix all regexes
document TypeConfig class
change version to beta
remove stale comment
better assert
change TypeConfig.update to updated
Merge pull request #97 from dimagi/type-configs

Type configs