Added a stub VCF parser -- only header is parsed for now
Updated 'Biocaml_vcf' to use 'Biocaml_lines' and added a simple test
Added a very basic VCF row parser
Implemented 'INFO' parsing in 'Biocaml_vcf'
Added 'FILTER' parsing to 'Biocaml_vcf'
Ensure uniqueness of VCF ids
Moar safety

  - Use 'safe' versions of 'int_of_string' and 'float_of_string'
  - Ensure 'REF' and 'ALT' values are valid DNA
Unified 'test_vcf', time for full-scale testing
Added a test for VCF sample from the spec.

  See http://www.1000genomes.org/wiki/Analysis/Variant%20Call%20Format/vcf-variant-call-format-version-41
Clarified unsupported features in 'Biocaml_vcf'
Merge from 'superbobry/v0.3-dev' (PR #81)

Fixed conflicts:
- src/lib/biocaml_lines.mli
  The diff was lost because of the documentation changes.