Simplifying and improving performance of Reader#read

Specifically, performance improvement is for reading multi-channel
files, reading mono files should have same performance.
Making buffer conversion faster in certain cases

Specifically, it takes the number of channels in the new and old
formats into account, in order to perform the bits-per-sample
conversion on the fewest number of samples.

For example, when converting stereo to mono, performing the bits
per sample conversion AFTER converting to mono will result in the
conversion operating on fewer samples. When converting mono to
stereo, performing the bits per sample conversion BEFORE converting
to stereo will also result in operating on fewer samples.
Adding support for reading/writing files with 24-bit PCM samples

Also allowing 24-bit buffers to be converted into different formats.
Adding link to the website to README
Properly reading a padding byte for chunks with odd sizes

According to the spec, all chunks should be aligned to an even
number of bytes, even if the number of data bytes is odd. This
was properly handled when reading the data chunk, but is now
handled for other chunk types as well.
Adding explanatory comment to test
Updating README and CHANGELOG with info about v0.6.0
Updating supported JRuby version in README
Giving credit
Improving bug fix description in README
Syncing README changes to CHANGELOG
Bumping version from 0.5.0 -> 0.6.0