Fix TypeScript buffer bug

[andrewmd5]

As outlined in #209, the TypeScript runtime utilizes a shared buffer for encoding which can lead to subtle bugs when decoding multiple types. For example:

    // should be the data of 'CreateUser'
    const createUserBuffer = CreateUser.encode({ email: "hi@andrew.im" });
    // encode another type
    CreateOk.encode({ now: 1 })
    // fails to decode as the data of 'createUserBuffer' is now the data of 'CreateOk.encode'
    const user = CreateUser.decode(createUserBuffer);

This change ensures we create and return a new buffer from 'toArray()'; yes, it allocates additional data, but it means users don't need to think about what happens when encoding multiple types when they might still need the data buffer.

[andrewmd5]

Holding off on merging this as it introduces a major performance hit

Bebop (subarray)   encode Song x 7,225,130 ops/sec ±0.08% (101 runs sampled)
Bebop (subarray)   decode Song x 2,861,336 ops/sec ±0.11% (100 runs sampled)
Bebop (slice)   encode Song x 2,259,026 ops/sec ±2.66% (80 runs sampled)
Bebop (slice)  decode Song x 2,823,515 ops/sec ±0.28% (94 runs sampled)

[andrewmd5]

opting for a different approach