added special 'property' field to columns

When defining a column, you can specify a "property" field
that will allow a more programmer-friendly name to be used
when selecting fields.

e.g.

var user = sql.define({
  name: 'user',
  columns: [{ state: 'state_or_province', property: 'state' }]
});

user.select(user.state);

README.md

@@ -76,7 +76,24 @@ var friendsWhoUseGmailQuery = user.from(userToFriends).where(friends.email.like(
 //LEFT JOIN "friendship" ON ("user"."id" = "friendship"."userId") 
 //LEFT JOIN "user" AS "friends" ON ("friendship"."friendId" = "friends"."id")
 //WHERE "friends"."email" LIKE %1
+```
+
+## Using different property names for columns
+```javascript
+var user = sql.define({
+  name: 'user',
+  columns: [{
+      name: 'id'
+    }, {
+      name: 'state_or_province',
+      property: 'state'
+    }
+  ]
+});
 
+//now, instead of user.state_or_province, you can just use user.state
+console.log(user.select().where(user.state.equals('WA')).toQuery().text);
+// "SELECT "user".* FROM "user" WHERE ("user"."state_or_province" = $1)"
 ```
 
 There are a __lot__ more examples included in the `test/dialects` folder.

lib/table.js

@@ -60,7 +60,8 @@ Table.prototype.addColumn = function(col) {
     console.log('Please notice that you have just defined the column "' + col.name + '". In order to access it, you need to use "table.getColumn(\'' + col.name + '\');"!');
   }
   this.columns.push(col);
-  this[col.name] = this[col.name] || col;
+  var property = col.property || col.name;
+  this[property] = this[property] || col;
   return this;
 };
 

test/table-tests.js

@@ -56,6 +56,27 @@ suite('table', function() {
   });
 });
 
+test('table with user-defined column property names', function () {
+  var table = Table.define({
+    name: 'blah',
+    columns: [{
+        name: 'id',
+        property: 'theId'
+      }, {
+        name: 'email',
+        property: 'uniqueEmail'
+      }]
+  });
+  var cols = table.columns;
+  assert.equal(cols.length, 2);
+  assert.equal(cols[0].name, 'id');
+  assert(cols[0] === table.theId, 'Expected table.theId to be the first column');
+  assert(table.id === undefined, 'Expected table.id to not exist');
+  assert.equal(cols[1].name, 'email');
+  assert(cols[1] === table.uniqueEmail, 'Expected table.uniqueEmail to be the second column');
+  assert(table.email === undefined, 'Expected table.email to not exist');
+});
+
 test('table with fancier column definitions', function() {
   var table = Table.define({
     name: 'blah',