IPv4 CIDR parser

<<Abstract:>> You must <<parse IPv4 subnets>> in CIDR notation and <<check>> whether <<IP addresses are part of>> a subnet or not. <<Note:>> The shortened form which leaves out trailing zeros is also considered valid. <<Introduction to subnetting:>> An IPv4 address (4*8 bits = 32 bits) is represented by four period separated bit octets. This means that 10.1.100.1 can be represented by 00001010.00000001.01100100.00000001. The subnet mask in CIDR notation describes the part of the IP address which cannot change (aka fixed bits). /24 describes 24 fixed bits which cannot change. The remaining 8 bits are used to generate IP addresses in this subnet. 11111111.11111111.11111111.00000000 is the equivalent subnet mask for /24 in binary (Greek: bi = two digits) and 255.255.255.0 in decimal (Greek: deca = ten digits) representation. Additional examples: 10.1.100.0/24 would allow to change the last bit octet and therefore are 10.1.100.255, 10.1.100.2, 10.1.100.20 valid examples which are part of this subnet. 10.1.101.1 isn't a valid example because 100 -> 101 is a change of the third octet which is forbidden by the subnet mask (aka fixed bits).