Merge branch 'release/0.2.4' into develop
Version back to 0.3.0
helpers: refactored template_def()
helpers: added template_argspec()
kernel: added argspec attribute to Module and Snippet
cluda/functions: more structured approach for sincos (now it is a function, not a snippet)

Fixes #7.
doc/history: added feature
cluda/functions: fixed norm() behaviour for non-complex arguments
test/cluda: added more tests for cluda.functions and separated them into their own module
doc/history: fixed a typo
test: moved core tests to a separate folder
TODO: updated tasks
helpers, cluda/kernel: creating a Template in a single place now
cluda/kernel: added a proper discovery protocol for modules and snippets
test/pytest_threadgen: moved reikna import inside a function so that it does not spoil coverage results
cluda: added ``strides`` keyword to array creation functions
cluda/kernel: using Singature objects instead of ArgSpec for snippet functions
cluda/tempalloc: using named tuples instead of AttrDict
test/helpers: changed diff_is_negligible() to make it easier to insert a debug print
test/helpers: added support for strided arrays in get_test_array()