Serial blosc

This is an extensive set of changes I have been working on. It fixes a major issue we where having integrating blosc with OpenVDB and Houdini.                                                                                                        
                                                                                                                
The issue we where running into is that blosc does not support multiple simultaneous users. By that I mean that if multiple users are calling into the blosc library from separate threads they both can not be processed at the same time. This is due to all the global variables protected by the global lock.                                                                                   
                                                                                                                
The solution we propose is to create a new API that works the way we  need it to. The api is currently sblosc_compress and sblosc_decompress.                                                                                              
                                                                                                                
Benifits of solution:                                                                                           
- Current API is preserved so current users of the blosc library need not modify their implementations.                                                                             
- New api will be easier for new users as there are only two functions needed for most of the work.                                                                                  
- Blosc_init and blosc_destroy are no longer needed.                                                            
- No more global used with the new API (old API still uses some globals, eventually these could be removed)                                                                   
- Support for both blosc internal threading and multiple simultaneous users. 
You are being too strict here IMO.  blosc_compress() and blosc_decompress() where the main functions before this PR.  I am not sure that we should deprecate them that fast mainly because one of its virtues is that one can tweak more Blosc internal parameters in the future without a need to change the API.

For example, I was able to add the `blocksize'  parameter by just adding the new blosc_set_size() function and not touching the original blosc_compress() / blosc_decompress().  There is merit on this, and in fact, the more that I think about that the more I would like this approach to be the recommended one.

What makes me a bit uncomfortable with the new blosc_compress_ctx() and blosc_uncompress_ctx() is that the parameter set is fix now and if in the future we would like to add more (say, a new filter), we will need to change the API.  Again, do you strictly need blosc_compress_ctx() and blosc_uncompress_ctx()?  Because if not, I would prefer to not introduce them in forthcoming Blosc 1.5.  Thoughts?