Bump version 0.5.0 -> 0.5.1

Trivial formatting change in README

Bump version to 0.4.9

Micro QR Code: allow empty content, if user requests it

QR Code: reduce encode time by about 8% (mask evaluation)

Telepen: allow empty content, if user requests it

Bump version to 0.4.5

Fix "Building" section formatting

Tag version 0.4.3

QR Code: add a few compaction efficiency sanity checks