Convtools

**Features**

- * introduced c.OptionsCtx
* improved tests - memory leaks
* improved docs - added the index page example; added an example to QuickStart

[convtools-ita 7](https://github.com/itechart/convtools/issues/7)

**Features**

- Introduced `labeling`:

* ``c.item("companies").add_label("first_company", c.item(0))`` labels the first
company in the list as `first_company` and allows to use it as
``c.label("first_company")`` further in next and even nested conversions

* ``(...).pipe`` now receives 2 new arguments:

* `label_input`, to put some labels on the pipe input data
* `label_output` to put labels on the output data.

Both can be either ``str`` (label name to put on) or ``dict`` (keys are label names
and values are conversions to apply to the data before labeling)

[convtools-ita 6](https://github.com/itechart/convtools/issues/6)


**Bugfixes**

- Added ``__name__`` attribute to ctx. Now internal code from the generated converter is sending to Sentry (not only file name).
Also the generated converter became a callable object, not a function.

[convtools-ita 5](https://github.com/itechart/convtools/issues/5)

**Bugfixes**

- Fixed ``c.group_by((c.item("name"),)).aggregate((c.item("name"), c.reduce(...)))``.
Previously it was compiling successfully, now it raises ``ConversionException`` on ``gen_converter``
because there is no explicit mention of ``c.item("name")`` field in group by keys (only tuple).

[convtools-ita 4](https://github.com/itechart/convtools/issues/4)

**Bugfixes**

- fixed ``c.aggregate`` to return a single value for empty input

[convtools-ita 3](https://github.com/itechart/convtools/issues/3)

**Bugfixes**

- ``c.aggregate`` now returns a single value (previously the result was a list of one item)

[convtools-ita 2](https://github.com/itechart/convtools/issues/2)

**Features**

- added ``c.if_`` conversion and introduced QuickStart docs

[convtools-ita 1](https://github.com/itechart/convtools/issues/1)


When v2 comes (if):

- the following reducers now raise `ValueError` if `initial` is passed:

* ArrayDistinct
* CountDistinct
* First
* Last
* MaxRow
* MinRow
* SortedArray
* Dict
* DictArray
* DictArrayDistinct
* DictCount
* DictCountDistinct
* DictFirst
* DictLast
* DictMax
* DictMin
* DictSum
* DictSumOrNone