Fix 'all' dependency in makefile

The 'all' target in the Makefile was messed up, causing 'make install'
to not see a normal 'make' as a dependency.
Change exit code of --help to be 0
Fix handling of --verbose long option

We were using some hybrid of letting getopt store the value of the --verbose
flag and trying to handle it ourselves, which was breaking the long option.
Add --version parameter
NULL terminate the longopts struct
Remove unnecessary DWARF* flags

DWARFCFLAGS and DWARFLIBS were no different than just adding to CFLAGS
and LIBS, removed.
Bump version to 1.1
Update link to libdwarf.rb gist
Add Travis-CI build status to README
Improve Travis CI config

- Add clang as a compiler
- Add './atosl --version' as a basic sanity test
Merge pull request #3 from zlandau/build_improvements

Build improvements