``mathtext`` has more sizable delimiters

The ``\lgroup`` and ``\rgroup`` sizable delimiters have been added.

The following delimiter names have been supported earlier, but can now be sized with

``\left`` and ``\right``:

* ``\lbrace``, ``\rbrace``, ``\leftbrace``, and ``\rightbrace``

* ``\lbrack`` and ``\rbrack``

* ``\leftparen`` and ``\rightparen``

There are really no obvious advantages in using these.

Instead, they are are added for completeness.

_ambi_delims=set(r"""

\Downarrow \Updownarrow . \vert \Vert""".split())

_left_delims=set(r"( [ \{ < \lfloor \langle \lceil".split())

_right_delims=set(r") ] \} > \rfloor \rangle \rceil".split())

_left_delims=set(r"""

""".split())

_right_delims=set(r"""

""".split())

def__init__(self):

'cwopencirclearrow' :8635,

'geqq' :8807,

'rightleftarrows' :8644,

'lgroup' :0x27EE,

'rgroup' :0x27EF,

'aa' :229,

'ac' :8766,

'ae' :230,

'leftparen' :40,

'rightparen' :41,

'bigoplus' :10753,

'leftbrace' :124,

'leftbrace' :123,

'rightbrace' :125,

'jmath' :567,

'bigodot' :10752,

r'$\sum x\quad\sum^nx\quad\sum_nx\quad\sum_n^nx\quad\prod x\quad\prod^nx\quad\prod_nx\quad\prod_n^nx$',# GitHub issue 18085

r'$1.$ $2.$ $19680801.$ $a.$ $b.$ $mpl.$',

r'$\text{text}_{\text{sub}}^{\text{sup}} + \text{\$foo\$} + \frac{\text{num}}{\mathbf{\text{den}}}\text{with space, curly brackets \{\}, and dash -}$',

]