added new base64(...) function to base64-encode binary data, along with a Base64Pipe <: IO type
add multimedia I/O mechanism (display, mm_write, and friends)
document BitArray methods and add ref-links for math-operators in base
Merge pull request #3932 from stevengj/mimedisplay

RFC: add multimedia I/O mechanism (display, mm_write, and friends); fixes #3817
faster max and min for float arrays
make float16 tables const
also remove trailing semicolons
add a few more common text MIME types