Merge pull request #15 from weese/feature/improve-bgzf-stream

[FIX] optimized BAM reading/writing
[FEATURE] added smart file as base class for BAM, BCF, GTF files
[FIX] adapted samcat for new smart file
[FIX] replaced SequenceFile by SmartFile<Fastq
[FIX] fixed bam demo
[FEATURE] added GffFileIn/Out
[FIX] fixed errors if zlib is not available, added getFileFormatExtensions() for SmartFile class
[FIX] first version of a heavy and lightweight BAM I/O context
[FIX] finished the heavy/lightweight I/O contexts and solved the owner/pointer problem
[FIX] fixed gff file demo
[FIX] fixed GFF context
[FIX] fixed BAM I/O context
[FIX] fixed samcat
[FIX] minor fixes
[FIX] 0-init GZ context