Fix citations
Add geometric distributions
Refactor tests for discrete distributions distributions
Add tests for geometric distribution
Rename function geometric to geometric0
in order to make names more symmetric
Add truncated exponential distribution
Remove unused Show constraints

They were used during debugging and were not removed
Add workaround for GHC bug #8072

GHC-7.6 have bug (#8072) which results in calculation of wrongs
number of buckets in function `uniformRange'. Consequently unformR
generates values in wrong range.

Bug only affects 32-bit systems and Int/Word data types. Word32
works just fine. So we set Word32 as unsigned counterpart for Int
and Word on 32-bit systems. It's done only for GHC-7.6 because
other versions are unaffected by the bug and we expect that GHC may
optimise code which uses Word better.

Fixes #25
Merge
Merge