Add IPLS ID3v2 frames to test mp3s
Prefer dot notation accessing the id3v2TagFrames

in specs, where feasible.
Shorten readId3v2TagContentFrame.. function names
Increase inspection depth in node example
Read ID3v2 tag's IPLS frames
Fix rogue whitespace
Add USER ID3v2 frames to test mp3s
Read ID3v2 tag's USER frames
Refactor lib's str/trm readers
Add expect-num-of-frames helpers in tests
Fix typo in browser example README
Improve documentation
Bump version patch number -> v0.2.4