Have related data-type converters in same namespace

[aryzing]

Is your feature request related to a problem? Please describe.

Helpers for converting between a Uint8Array and its hex-encoded string representation should probably be within the same namespace. Currently, seems the only way to convert between the two formats is to use helpers in different namespaces:

• encode.buf2hex()
• num.hexToBytes()

Describe the solution you'd like

Possibly have hexToBytes() and bytesToHex() helpers both living in the encode namespace, although anything that makes them easier to find would be fine.