Added generic_{integer,float,string,boolean}_info_field methods.
Updated test_variants.vcf with new info annotations.
More use of auto, using iterator constructor, and template function for int32_t / float generic_info_field.
Fixed typo to use free instead of delete on malloc memory.
Merge pull request #82 from broadinstitute/ks_info_field

Added generic_{integer,float,string,boolean}_info_field methods.
New has_format_field() checking if given format field in header.
New unit test to it.

changed name has_field() to has_format_field().

updated variant_header_test with has_format_field.