Check size of enriched.out.json before indexing

- Pass argument to main method of Index.java to specify minimum
size of file to index
- Refuse to index if file is smaller
- Prevent building an empty index or an index with only a subset
of the available data
Make transformation of Sigel updates more robust

- Make sure that at least one interval (specified start until
today) is loaded; this is crucial if the specified interval size
is smaller than the time span between start and today
- Always stop with the date of today (no future dates), i.e. make
last interval a bit longer or shorter
Update README.textile
Merge pull request #22 from SBRitter/index-update

Make updates and indexing more robust