Convtools

**Bugfix**

- fixed [2](https://github.com/westandskif/convtools/issues/2): issue with
input args passed to pipe labels

**Misc**

- hard fork

**Bugfix**

- fixed passing strings containing ``%`` and ``{`` to ``c.aggregate`` -
- [convtools-ita 34](https://github.com/itechart/convtools/issues/34)

**Bugfix**

- replaced ``linecache`` populating code with real dumping generated code to
files in either ``PY_CONVTOOLS_DEBUG_DIR`` (*if env variable is defined*) or
to python's ``tempfile.gettempdir``. This adds pydevd support (VS Code and PyCharm debugger).

**Features**

- introduced ``c.breakpoint`` and ``(...).breakpoint()`` to simplify debugging long pipelines

**Misc**

- [internals] created a separate conversion for ``c.this()``
- [internals] now ``c.naive`` is a direct init of ``NaiveConversion``
- improved quick start, cheatsheet and api docs

**Bugfix**

- fixed piping something complex to ``c.join``

**Misc**

- [internals] reworked aggregate & group_by templating
- [internals] reworked optional items processing