Support for index definition key (columns)

[DQinYuan]

For issue #51

like mysql

CREATE TABLE `table10_int_autoinc` (
   `col_float_key` float, 
   `col_time_key` time, 
   pk integer auto_increment,  
   key (`col_float_key`), 
   key (`col_time_key`), 
   primary key (pk))

will be equivalent to

CREATE TABLE `table10_int_autoinc` (
   `col_float_key` float, 
   `col_time_key` time, 
   pk integer auto_increment,  
   key `col_float_key` (`col_float_key`), 
   key `col_float_key`  (`col_time_key`), 
   primary key (pk))

and

CREATE TABLE `table10_int_autoinc` (
   `col_float_key` float, 
   `col_time_key` time, 
   pk integer auto_increment,  
   key (`col_float_key`, `col_time_key`), 
   primary key (pk))

will equivalent to

CREATE TABLE `table10_int_autoinc` (
   `col_float_key` float, 
   `col_time_key` time, 
   pk integer auto_increment,  
   key `col_float_key`  (`col_float_key`, `col_time_key`), 
   primary key (pk))

[coveralls]

Coverage decreased (-0.6%) to 88.141% when pulling 70e29e6 on DQinYuan:master into 1203878 on xwb1989:master.