Rename "Micro-Bitcoin" to "Zibcoin"

*  The lengthy word "microbitcoin" is abbreviated as "zibcoin" or just "zib".

*  The three letter code for zibcoin is "ZBC".

*  "Millibitcoin" is updated accordingly, to "kilozibcoin" or just "k zib", because multiples are more intuitive than fractions.
Merge pull request #1 from zibcoin/zibcoin-units

Rename "Micro-Bitcoin" to "Zibcoin"