SourceLayout: Shuffle ident files into libident.la

SourceLayout: Shuffle ident files into libident.la

 * Moves files into ident/ for library
 * Adds Ident:: namespace for interface.
 * Moves ident config to Ident::TheConfig
 * reduces one avenue of memory leak on double-Init of ident objects.
 * Makes ident ACL only relevant when ident is available
 * Wraps Ident code in USE_IDENT for monolithic or empty library build
 * Adds documentation for ident API

TODO: Async and Object'ify the ident internals.