proper error handling, type::name objects now stored with leading /, and new option to disable Perl magic

lib/App/HostScript.pm:
* added option for new, use_perl, which defaults to 1 and if 0 turns off the perl magic
* added keys to $self: global (type::false), position (0), stopped (0), execstack ([]), $error (type::dict({})), and errordict (a hash representing default errordict)
* added sub _get_errordict with helper subs _set_generic_error and _terse_dstack
* changed die messages in _number_test, _number_pair_test, _get_systemdict
* prepended keys in _get_systemdict with /
* added keys /stop and /setglobal in _get_systemdict
* /def in _get_systemdict no longer strips the leading /
* Perl magic does not get loaded into systemdict if use_perl is false
* renamed Perl magic /load to /use because of PostScript operator conflict
* added error checking to /eval, /use, and /new
* _parse_token returns without processing if $self->{stopped} is true
* _parse_token skips Perl magic if use_perl is false
* significant changes to execution of type::name objects,
* removed feature of names starting with $ being special - just use eval
* sub decode sets $self->{stopped} to false after parsing all tokens
* added sub test_decode which is like decode, but dies if $self->{stopped} is true
* sub run sets $self->{stopped} to false after parsing all tokens
* updated documentation

lib/App/HostScript/type.pm:
* type::name->new returns what was passed if it is already of type::name
* type::dict->new now also accepts an ARRAY with an even number of values
* type::dict->new no longer strips the leading / from a type::name object

t/10_load.t:
* changed operator 'load' to 'use' in test HostScript code

t/TestMLBridge.pm:
* changed decode to test_decode in sub pson_decode

t/testml/load.tml:
* changed keys in json to start with /