Make browser-compatible, reduce allocations during encoding and decoding

[liamdon]

1. Replace direct usage of node.js Buffer API to allow the library to work in both browser and node environments

2. Improve performance by not allocating buffer in every encode call and v in every decode call - instead use one preallocated buffer for both cases. This is safe because:

• Both buffer and v always have length 26
• Every element is written
• Both are internal and are not returned to the caller, so don't need a unique reference.

[ongteckwu]

Thank you makes a lot of sense.

[ongteckwu]

Updated to v0.2.8