VarNumDecodes

Decode variable-length integer which has maximum bits of maxBits.

Quoting from https://wiki.vg/Protocol,

 > These are very similar to Protocol Buffer Varints: > the 7 least significant bits
are used to encode the value > and the most significant bit indicates whether there's
another byte after it > for the next part of the number. > > The least significant group is
written first, followed by each of the more significant groups; > thus, VarInts are
effectively little endian (however, groups are 7 bits, not 8). 

For example, consider the following byte stream obtained from network whose head is expected to be a variable-integer:

 10001001 10010101 01111000 10100111 ... 

Since third byte has the most significant bit set to zero, variable-integer data ends here.

 X0001001 X0010101 X1111000 | 10100111 ... 

Lower 7 bits from each byte is aggregated, and we obtain little-endian 7bit blocks:

 0001001 0010101 1111000 0000000 0000XXX 

In big endian 8bit blocks, this data corresponds to

 00000000 00011110 00001010 10001001 

A decoder that reads a VarLong data and output the value as an Long.

A decoder that reads a VarInt data and output the value as an Int.