Added size{Less,Greater}ThanOrEqual functions, and using these in place of manual +/-1 calls which were not Long-overflow safe.

Also fixed performance bug where .take would not bail early when the number of bits taken exceeded the size of a subtree.
Merge pull request #7 from scodec/topic/size-lessThanOrEqual

Added `size{Less,Greater}ThanOrEqual` functions, and using these in place ...