[buffer] Remove implemented TODOs
[buffer] Handle negative length construtor parameter
[buffer] Handle {length: N} as constructor parameter

For some reason Node.js supports that.
[buffer] Fix size limit handling for hex encoding
[buffer] Fix size limit handling for base64 encoding
[buffer] Fix handling of unmatched Unicode surrogates
[buffer] Rename method_readInt() into method_readInteger()
[buffer] Implement readDouble/FloatBE/LE() methods