Added a method to write variable sized unsigned values. Use this method for

Added a method to write variable sized unsigned values. Use this method for
all sorts of things in the object files. This does not only make the object
files smaller, but does also remove several limits (strings may be longer
than 255 bytes, several counters no longer have 8 or 16 bit limits).

git-svn-id: svn://svn.cc65.org/cc65/trunk@260 b7a2c559-68d2-44c3-8de9-860c34a00d81