Merge pull request #4 from alexeyvo/compress_encrypt

Implement compressing\decompressing using zlib while reading\writing cnv gridfs stream
Merge pull request #5 from alexeyvo/compress_encrypt

Reimplement compress feature to compress each chunk for allow seek
Merge pull request #6 from alexeyvo/compress_encrypt

Update readme
B-0 removed reference to vld.h file
B-0 added proper casts to remove warnings due to datatype conversions
B-0 added cast to prevent warning when compiling in 64 bits
B-0 removed warning compiling in 64 bits with casts from 64 bits integers to 32 bits
Merge pull request #7 from jsbattig/fix_compilation

Fix compilation and warnings
Implement encryption of file