Don't fail parsing ALTER TABLE ADD COLUMN ending with a semicolon - #246

Since PR apache#93
`parse_column_def` parses a set of column options in a loop, e.g. given:

```
                  _______ column_def _______
CREATE TABLE foo (bar INT NOT NULL DEFAULT 1, )
                          -------- ---------
                          option 1  option 2
````

it parses column options until it encounters one of the delimiter tokens

First when we only supported `CREATE TABLE`, the set of delimiters that
stopped the parsing used to be `Token::Comma | Token::RParen`.

Then we added support for `ALTER TABLE ADD COLUMN <column_def>`. Turns
out the parser started to bail if the statement ended with a semicolon,
while attempting to parse the semicolon as a column option, as we forgot
to add it to the set of delimiter tokens.

This was recently fixed in apache#246
by including Token::SemiColon to the list, but it felt wrong to have 
to update this list, and to have a common list of delimiters for two
different contexts (CREATE TABLE with parens vs ALTER TABLE ADD COLUMN
without parens).

Also our current approach cannot handle multiple statements NOT
separated by a semicolon, as is common in MS SQL DDL. We don't
explicitly support it in `parse_statements`, but that's a use-case
like to keep in mind nevertheless.

Since PR apache#93
`parse_column_def` parses a set of column options in a loop, e.g. given:

```
                  _______ column_def _______
CREATE TABLE foo (bar INT NOT NULL DEFAULT 1, )
                          -------- ---------
                          option 1  option 2
````

it parses column options until it encounters one of the delimiter tokens

First when we only supported `CREATE TABLE`, the set of delimiters that
stopped the parsing used to be `Token::Comma | Token::RParen`.

Then we added support for `ALTER TABLE ADD COLUMN <column_def>`. Turns
out the parser started to bail if the statement ended with a semicolon,
while attempting to parse the semicolon as a column option, as we forgot
to add it to the set of delimiter tokens.

This was recently fixed in apache#246
by including Token::SemiColon to the list, but it felt wrong to have
to update this list, and to have a common list of delimiters for two
different contexts (CREATE TABLE with parens vs ALTER TABLE ADD COLUMN
without parens).

Also our current approach cannot handle multiple statements NOT
separated by a semicolon, as is common in MS SQL DDL. We don't
explicitly support it in `parse_statements`, but that's a use-case
like to keep in mind nevertheless.

Since PR apache#93
`parse_column_def` parses a set of column options in a loop, e.g. given:

```
                  _______ column_def _______
CREATE TABLE foo (bar INT NOT NULL DEFAULT 1, )
                          -------- ---------
                          option 1  option 2
````

it parses column options until it encounters one of the delimiter tokens

First when we only supported `CREATE TABLE`, the set of delimiters that
stopped the parsing used to be `Token::Comma | Token::RParen`.

Then we added support for `ALTER TABLE ADD COLUMN <column_def>`. Turns
out the parser started to bail if the statement ended with a semicolon,
while attempting to parse the semicolon as a column option, as we forgot
to add it to the set of delimiter tokens.

This was recently fixed in apache#246
by including Token::SemiColon to the list, but it felt wrong to have
to update this list, and to have a common list of delimiters for two
different contexts (CREATE TABLE with parens vs ALTER TABLE ADD COLUMN
without parens).

Also our current approach cannot handle multiple statements NOT
separated by a semicolon, as is common in MS SQL DDL. We don't
explicitly support it in `parse_statements`, but that's a use-case
like to keep in mind nevertheless.