fix: using the Format tag on bitfield members now throws an exception
added experimental ByteOrder tag
added ELF parser example
improve internals
o better encapsulation of the pack/unpack code
o avoid unneccessary computations
o thanks to the cachegrind tool (http://valgrind.org), some expressions in the lexer code of the ucpp preprocessor could be optimized, making the preprocessor more than 10% faster on x86 platforms; this means that parsing should be about 7% faster now