[A] Added adding_strategy property to the tables

[seleznevae]

This functionality partially helps to resolve questions from #28 .

[coveralls]

Pull Request Test Coverage Report for Build 655

• 192 of 245 (78.37%) changed or added relevant lines in 8 files are covered.
• 12 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.3%) to 78.601%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/table.c	7	8	87.5%
src/vector.c	42	47	89.36%
src/fort_impl.c	33	44	75.0%
src/row.c	41	55	74.55%
tests/bb_tests_cpp/test_table_basic.cpp	0	22	0.0%

Files with Coverage Reduction	New Missed Lines	%
tests/bb_tests_cpp/test_table_basic.cpp	1	0.0%
src/properties.c	2	88.85%
tests/bb_tests/test_memory_errors.c	2	84.93%
src/fort_impl.c	7	88.62%

Totals
Change from base Build 652:	-0.3%
Covered Lines:	4507
Relevant Lines:	5734

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💛 - Coveralls