copy edits 2 from Robbie

[robbiemorrison]

some more tweaks, comprising:

• the two copyright notices now corrected and aligned (one in text, one in footer)
• minor copy-edits (some optional, some probably mandatory, thus marked)
• one improved definition (actually digital|software × object|artifact could be rationalized further)
• one significant markdown error
• cleaning up of text files (trailing spaces, multiple blank lines)
• cleaning up of license notice (tabs to single space chars, maybe you do not want to do that)

good luck!

[rdicosmo]

Thanks @robbiemorrison , I checked all commits, and I'm going to merge them.