AIGER writer

[hriener]

This PR implements a simple version for writing combinational AIG networks into the binary AIGER format.

[coveralls]

Pull Request Test Coverage Report for Build 272339525

• 36 of 42 (85.71%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.008%) to 79.505%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
include/mockturtle/io/write_aiger.hpp	36	42	85.71%

Files with Coverage Reduction	New Missed Lines	%
include/mockturtle/algorithms/akers_synthesis.hpp	1	97.48%
include/mockturtle/algorithms/dsd_decomposition.hpp	3	87.5%

Totals
Change from base Build 244605707:	-0.008%
Covered Lines:	9407
Relevant Lines:	11832

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💛 - Coveralls