TTTTimeIntervalFormatter's precision can be specified

Adds `numberOfSignificantUnitsToDisplay` and `leastSignificantUnitToShow` properties.
Adds assertion in setLeastSignificantUnitToShow:
Better naming consistency.
AppleDoc comment style more consistent with rest of project.
Add localizations to sub spec instead of the spec

This way, they will included if you only ask for a specific sub spec
Missing MD code block in README

Added missing code block in "Speen in Imperial Units with Bearing in
Degrees" example
Merge pull request #53 from xHunter/master

Missing code block in examples
Merge pull request #52 from mirego/add-localizations-to-subspecs

Add localizations to sub spec instead of the spec
de
Merge pull request #55 from BlackLee/master

Add a percent symbol for German
Merge pull request #51 from defragged/specify-precision

TTTTimeIntervalFormatter: Specifying Precision
Improving organization of docs headers
[Issue #51] Dropping 'ToDisplay' from new properties' names
Bumping version to 1.2.0
Removing unnecessary validations
Fix else if in TTTTimeIntervalFormatter
Merge pull request #56 from JoshTheGeek/patch-1

Fix else if in TTTTimeIntervalFormatter
Merge remote-tracking branch 'upstream/master' into develop