Convtools

**Bugfixes**

- fixed aggregate issue: reduce(...).item(..., default=...) case [convtools-ita 15 ](https://github.com/itechart/convtools/issues/15)

**Bugfixes**

- fixed Aggregate multiple reduce optimization
- added main page
- added workflow example

[convtools-ita 14](https://github.com/itechart/convtools/issues/14)

Updated index page docs.

**Features**

- - increased the speed of ``c.aggregate`` and ``c.group_by`` by collapsing multiple ``if`` statements into one
- updated labeling functionality

[convtools-ita 11](https://github.com/itechart/convtools/issues/11)

**Features**

- Improved the way ``linecache`` is used: now the number of files to be put
into the ``linecache`` is limited to 100. The eviction is done by implementing
recently used strategy.
[convtools-ita 9](https://github.com/itechart/convtools/issues/9)
- - introduced ``c.join``
- improved & fixed pipes (code with side-effects piped to a constant)

[convtools-ita 10](https://github.com/itechart/convtools/issues/10)

**Features**

- 1. fixed main example docs
2. improved ``c.aggregate`` speed

[convtools-ita 8](https://github.com/itechart/convtools/issues/8)