libhackrf: refactor serial number searching to hackrf_open_usb()

Create a #define/constant for the usb_descriptor_string_serial_number length.

Refactor obtaining LPC serial number and chip ID into separate API and header/source files. Remove from main().

Serial number firmware and host-side changes. Very hacky at this point.

nudged refs for assembly diagram

updated DFU make instructions

removed .svn directory that never should have been there

Merge pull request #150 from jboone/hotfix_compiler_warnings_20141110

Re-scope buffer[] to solve unread array warning.

XSVF: Fix apparent #ifdef scope bug in xsvfDoXCOMMENT() where comments aren't truly ignored.