Package buffer contains buffer and wrapper types for byte slices. It is useful for writing lexers or other high-performance byte slice handling. The `Reader` and `Writer` types implement the `io.Reader` and `io.Writer` respectively and provide a thinner and faster interface than `bytes.Buffer`. The `Shifter` type is useful for building lexers because it keeps track of the start and end position of a byte selection, and shifts the bytes whenever a valid token is found. The `Lexer` is however an improved version of `Shifter`, allowing zero-copy for the parser by using a (kind of) ring buffer underneath.