update ubuntu install instructions

The previous install instructions failed with `apt-add-repository: command not found`. To resolve this we need to install two packages as described [here](http://askubuntu.com/a/38035).
Merge pull request #72 from kylewest/patch-1

update ubuntu install instructions
updating contributors #72
alredy
Merge pull request #77 from szepeviktor/patch-1

typo: alredy
Workaround module for old versions of Digest::SHA

Digest::SHA prior to 5.63 has problems with large data chunks 1GB (or 512Mb?) on 32/64bit machines.
feeding data by chunks, then.
SHAHash - rename to large_sha256_hex
Intergare large_sha256_hex
gemu - additional validation for sha256
benchmark/ dir and first benchmark
improve benchmark
Removing old workaround for old buggy Digest::SHA
SHAHash - shortcircuit for new Digest::SHA versions
gemu-test - increase timeouts, print more debug info
Merge branch 'master' into development
Merge branch 'digest_sha_workaround_remove_old_workaround' into development