created TermGroup.pm with test file

TermGroup.pm represents a single <termGroup> element. It contains only
simple scalars, so I have used Class::Accessor to generate all of the
functionality. Each accessor and the constructor are documented, and
other POD such as the SYNOPSIS have been added as necessary.

The test file checks the constructor and all accessors for correctness.
created LangGroup.pm with test file

LangGroup.pm represents a single <langGroup> element of TBX-Min. It
contains a single scalar (its language), along with an accessor for
the contained term groups.

I chose to return the internal array reference for the term groups
because it seemed like it might be unwieldy to also provide
remove_term_group and clear_term_groups.

The term_groups accessor croaks on input so as to avoid confusion with
the getter/setter accessors in TermGroup.pm.
created ConceptEntry.pm with test file

ConceptEntry.pm represents a single <conceptEntry> element of TBX-Min.
It contains a single scalar (its id), along with an accessor for
the contained language groups.

I chose to return the internal array reference for the language groups
because it seemed like it might be unwieldy to also provide
remove_lang_group and clear_lang_groups.

The lang_groups accessor croaks on input so as to avoid confusion with
the getter/setter accessors in TermGroup.pm.

The test file checks the constructor and both accessors.
use 'code' instead of 'lang' in LangGroup

Changed the 'lang' method to 'code' because the word 'code' is more
clearly the language abbreviation than is the string 'lang'. Besides,
in the future we may need to return the full language name, and then
'lang' would be a confusing name for the abbreviated name.
fixed id check in ConceptEntry test

The test for the id method was not actually checking much, since
$args->{id} did not exist. I suppose it was checking that setting the
id to undef leaves it undef, but since that is the default value it
doesn't help much.

Now id is set to a real string, and the return value of the id method
is checked and found not to be undef.
Working Min.pm and XML reading tests

Min.pm now fully parses a TBX-Min file, and 01-read.t passes all tests.
In the test file, names of classes were updated to their current forms,
and certain methods were similarly updated. The file also tests that a
string pointer can be parsed, and it has been renamed to have a
properly ordered number and to reflect its function better.