Add field class/type/length to info output for list-fields

[nalinigans]

Enhanced information for genomicsdb_query -w <ws> --list-fields. e.g.

./genomicsdb_query -w ws --list-fields
Field                Class      Type       Length
-----                -----      ----       ------
GQ                   FORMAT     Integer    1
GT                   FORMAT     Integer    PP
BAF                  FORMAT     Float      1
LRR                  FORMAT     Float      1
MIN_DP               FORMAT     Integer    1
PGT                  FORMAT     String     VAR
PID                  FORMAT     String     VAR
PL                   FORMAT     Integer    G
RGQ                  FORMAT     Integer    1
SB                   FORMAT     Integer    4
DS                   FORMAT     Float      1
HDS                  FORMAT     Float      2
GP                   FORMAT     Float      3
PASS                 FILTER     Integer    1
AF                   INFO       Float      A
AQ                   INFO       Integer    A
AC                   INFO       Integer    A
AN                   INFO       Integer    1
AD                   FORMAT     Integer    R
DP                   FORMAT     Integer    1
RNC                  FORMAT     Char       2
--
Abbreviations : 
  A: Number of alternate alleles
  R: Number of alleles (including reference allele)
  G: Number of possible genotypes
  PP or P: Ploidy
  VAR or var: variable length

[mlathara]

lgtm