Issue 50: Use standard chef/knife formatting for all knife decrypt output

Fixes #50: Use standard chef/knife formatting for all knife decrypt output

Went through files and removed use of brackets where command-line arguments are mandatory.  Left brackets in where arguments are optional.

Minor formatting - whitespace removal, fixed an indent on a def.

Updated README.md and KNIFE_EXAMPLES.md to include formatting options.

If you guys want me to add the brackets back in, I can ammend these commits.  I just know when we started using chef-vault, there were rumblings from some of us about the use of brackets on mandatory arguments ;)