fix links in README
developerguide.adoc: add AsciiDoc attributes (TOC, icons, imagesdir)
developerguide.adoc: fix integer decode example
developerguide.adoc: fix math in explanation

The synchronization sequence used to be 0x55 0x55 0xff 0xff,
which is where the 65535 came from.
Merge pull request #30 from jboecker/developerguide-edits

Developer Guide updates