support for hive variables

Although unit tests pass, the following example fails:
```
$ ./run-test.sh artist-count
```
because the ${table} variable is not injected .e.g
```
INFO: NoViableAltException(16@[183:1: tableName : (db= identifier DOT tab= identifier -> ^( TOK_TABNAME $db $tab) |tab= identifier -> ^( TOK_TABNAME $tab) );])
...
INFO: FAILED: ParseException line 2:21 cannot recognize input near '$' '{' 'table' in table name
```