Change Fibder to Fiber

Change fortmat to format.

mrbc: use binary mode on outfile

This solves the problem of incorrect bytecode generated by mrbc
for single files on Windows platform (which is by default text-mode)

removed unused variables / assigns never used

Changed the object_count so that it only iterates over the RBasic object, not the full RVALUE known by the GC

Fix compiler warning by exiting if wfp isn't set

Fix for issue 1243

add comments for mruby-array-ext