Provides some functions for working with Young diagrams.

- partitionsequence: computes partition sequence for an integer partition
- a \ b creates the skew diagram for partitions (tuples) a, b
- isrimhook: checks if skew diagram is a rim hook
- leglength: computes leg length of rim hook
- character: computes character of irrep of Sn
Merge pull request #6 from jiahao/young

Provides some functions for working with Young diagrams.
Add partitions function
Update README for partitions
Rename and add tests for the partitions function

As there is already an integer_partitions function in Base which
does basically the same thing, it is better to have this as an
extra method of it.
Rename types to use CamelCase
Update README.md with the new name of the function
Update the library to work with the recent changes to BigInt