Retrieve ancentors of a given term

## Getting parent terms and/or ancestor ones

1. Get all the ancestor terms of a given term.
2. Get the only the parent terms of a given term.

1. Get all the ancestor terms of a given term:

       			use OBO::Parser::OBOParser;

       			my $my_parser = OBO::Parser::OBOParser->new();
       			my $ontology = $my_parser->work("my_obo_ontology.obo");

       			my $interesting_term = $ontology->get_term_by_name("protein");

       			my @descendents = @{$onto->get_ancestor_terms($interesting_term)};

       			foreach my $t (@descendents) {
       				print "The name of the ancestor term is: ", $t->name();
       			}

2. Get the only the parent terms of a given term:

       			use OBO::Parser::OBOParser;

       			my $my_parser = OBO::Parser::OBOParser->new();
       			my $ontology = $my_parser->work("my_obo_ontology.obo");

       			my $interesting_term = $ontology->get_term_by_name("protein");

       			my @children = @{$onto->get_parent_terms($interesting_term)};

       			foreach my $t (@children) {
       				print "The name of the parent term is: ", $t->name();
       			}