Grow in and around pair and tag text objects

Grow visual selections by repeating pair and tag text objects:
```
vi(i(a vi)i)a vibiba    va(a(a va)a)a vababa
vi{i{a vi}i}a viBiBa    va{a{a va}a}a vaBaBa
vi[i[a vi]i]a virira    va[a[a va]a]a varara
vi<i<a vi>i>a viaiaa    va<a<a va>a>a vaaaaa
vitita                  vatata
```

Closes #41.