Merge branch 'release/0.5.2' into develop
Next version is 0.6.0
setup: added sphinx to dev dependencies
cbrng/samplers.mako: casting component_std to r_dtype
transformations: added norm_param() and norm_const()
TODO: rearranged tasks

Need to make a semi-major release.
test/computations/reduce: removed a debug line
doc/history: fixed a reference
norm: added the EntrywiseNorm computation
A big move of several computation submodules to thematic subpackages
TODO: removed a task
test/cbrng/cbrng: fixed an import
cbrng/samplers: fixed a bug introduced by commit #ef1b6d8df8
core/signature: not casting a scalar argument if it already has the target dtype
core/transformation_modules: casting the possible module object to string to get the prefix
cluda/dtypes: cast() now checks for dtype to avoid unnecessary casts
cluda/dtypes: normalizing dtypes before processing
cluda/dtypes: added support for multi dimensional arrays in struct dtypes
reikna/transformations: added a stub transformation
reikna/transformations: added broadcasting transformations