Simple locators

We could write:
```python
"#url"
# instead of
"//*[@id='url']"
```
```python
".someclass"
# instead of
"//*[contains(@class, 'someclass')]"
```
and so ...

It is limited to a subset of CSS selectors, useful for selecting "single" (in means of no hierarchical selector) elements eg. in forms.:
* #someid
* .someclass
* input#someid
* div.someclass
* div#myid.not-dimmed
* div.class1.class2

And so...