partially refactored ABIF header reading
collected: struct reading

We can read the whole structure at once
added reading entries from data directory
added some checks, changed int to uint32_t, short to uint16_t
I've tried to read data manually - doesn't help
Merge branch 'bioruby_experiments-2013-10-16'
fixed reading problem with big-endian encoding!!!!!!
Merge branch 'master' into bioruby_experiments-2013-10-16