Support for Number=A in INFO

[brentp]

http://www.1000genomes.org/wiki/Analysis/Variant%20Call%20Format/vcf-variant-call-format-version-41
Says:

The Number entry is an Integer that describes the number of values that can be included with the INFO field. 
For example, if the INFO field contains a single number, then this value should be 1; if the INFO field describes
 a pair of numbers, then this value should be 2 and so on. If the field has one value per alternate allele then this
 value should be 'A'; if the field has one value for each possible genotype (more relevant to the FORMAT tags)
 then this value should be 'G'.  If the number of possible values varies, is unknown, or is unbounded, then this 
value should be '.'. 

This is addressed in this commit along with a misspelling of RESERVED_FORMAT