This commit removes all .gitkeep files from the ATS directory. ETSI
deliverables should not contain empty directories or non relevant files
such as .MACOSX or .gitkeep.

Test Sem_160106_the_not_implemented_function_005 verified that `???`
always yields the same results.
However, there's no such requirement specified. Furthermore, `???` may
throw an error when executed, which is also not covered by this test.

V15 unvalidated Fokus

See merge request !3

V15 unvalidated Elvior

See merge request !4

V15 unvalidated Nokia

See merge request !5

Resolve "Nested types"

Closes #6

See merge request k3/ttcn3-conformance-tests!7

Resolve "Automatic type for index assignment lists."

Closes #5

See merge request k3/ttcn3-conformance-tests!6

Resolve "Automatic type for field assignment list"

Closes #2

See merge request k3/ttcn3-conformance-tests!5

Resolve "Automatic type for value lists"

Closes #4

See merge request k3/ttcn3-conformance-tests!4

Resolve "Automatic types for expressions"

Closes #3

See merge request k3/ttcn3-conformance-tests!3

Aktualisieren ATS/core_language/19_basic_program_statements/1902_if_else_statement/Sem_1902_if_else_statement_003.ttcn, ATS/core_language/19_basic_program_statements/1903_select_statements/190301_select_case_statement/Sem_190301_select_union_statement_008.ttcn, ATS/core_language/19_basic_program_statements/1903_select_statements/190302_select_union_statement/Sem_190302_select_union_statement_007.ttcn, ATS/core_language/19_basic_program_statements/1905_while_statement/Sem_1905_while_statement_004.ttcn

Aktualisieren ATS/core_language/A_BNF/A0102_TrailingCommas/Syn_A0102_TrailingCommas_001.ttcn, ATS/core_language/27_specifying_attributes/2701_attribute_mechanism/270101_scope_of_attributes/Syn_270101_ScopeOfAttributes_005.ttcn

Add variadic functions

See merge request k3/ttcn3-conformance-tests!2