support binary format of integers, e.g. 0b00101

[p4l1ly]

implements feature #113

[chyh1990]

According to the yaml 1.1 spec, https://yaml.org/type/int.html

Integer can use binary representation and can contain separator _.

But according to 1.2 spec, binary representation of integer seems to be deprecated,

1.2 spec (section 10.3. Core Schema) lists only three regex format for int type:

[-+]? [0-9]+ | tag:yaml.org,2002:int (Base 10)
-- | --
0o [0-7]+ | tag:yaml.org,2002:int (Base 8)
0x [0-9a-fA-F]+ | tag:yaml.org,2002:int (Base 16)

so in 1.2, 0b0101 should be interpreted as string, instead of int. This library is designed for yaml 1.2, so current behavior is expected and should be kept.