allow to override default OpenCL compile options by defining CLFFT_COMPILE_OPTIONS macro

See merge request !6

Add clFFT_GetSize() for getting the estimated size of a plan

See merge request !5

- similar to cufftGetSize()

Remove GPU constraint

See merge request !4

Makefile improvements

See merge request !3

- allow to build shared and static versions separately

- fix OSX shared build

add a shared library version

See merge request !2

renamed library and header to 'eclfft' to avoid conflicts with clFFT

See merge request !1

- this installs the header in $PREFIX/include/eclfft and the lib in $PREFIX/lib/eclfft.a

Switching to archive files (OpenCL.lib for 64 bit seems to be compiled to a different/incompatible format)

fixed previous commit for C99 compliant float printf format

-fixed compilation warning
-fixed problem of using "%a" printf-format which is only supported in C99 and later, which cannot be assumed for mingw
 cross compiles for Windows. Now uses this format only conditionally if supported, otherwise falls back to %f for
 generated float literals

added file comment headers to express that this is now derived work and not the original Apple source code
The original Apple comment headers with (c) and license info are retained

Prevent integer overruns for long transforms in Taylor approx of sin cos.
Still to do: check all uses of mad24 etc in generated code where overruns could occur as well

fix: use compiler flag to globally convert all double constants to floats

added plan class creation method that allows to set flags to direct code generation
currently limited to select among 4 methods to compute twiddle factors:
-native_sin,native_cos function
-sincos() function
-set of two LUTs in global memory
-Taylor series approx via a smaller LUT in shared memory

experimanetal: improved Taylor series approx by copying LUT to shared mem.
               TODO: cleanup, expose sin/cos method on plan creation interface,
                     do proper calculation of available shared mem for sin cos LUT

experimental: -added alternative method for twiddle factor calc, using a smaller LUT (256 * float2 )
               via Taylor series to 3rd order, seems to be almost as accurate as method with 2 bigger LUTs, but faster.
              -improved method w/ 2 bigger LUTs to use LUTs of float2
              -improved method using slow sin/cos functions (now uses sincos combined function), still slow
              - preparaed plan struct to have method switchable at plan creation time.

              TODO: load smaller LUT for Taylor series approx into shared mem.

Still experimental: replace calls to native_sin in clFFT
This change explores the performance impacts of using a set of LUTs, precomputed on the CPU
to perform sin(x_i) and cos(x_i) in a grid x_i= +/- 2*pi *i/N , N fixed.

On a 6770M, this code is still ca 3% slower than the original native_sin/native_cos varaint
for a BRP4-like transform

This variant should have a very high accuracy, versions with lesser accuracy but
higher performance should be explored next. Eventually the method should be selectable
by a parameter to the plan creator as suggested by Bernd.

TODO: - remove some diagnostic code,
      - optimze total size of LUTs perhaps by using
        cos(x) = sin(x+pi/2), so no need to keep separate LUTs for sin and cos, just one slighly longer with
        an additional alias pointer
      - try caching the LUTs in shared memory (using constant memory didn't help)

* Supported targets: linux (default), macos, win32, clean