Pyslvs-ui

**Development**:

+ This version has been skipped.

**Features**:

+ "External loop" layout for atlas of structural synthesis.
+ Other layout functions are removed from option.
+ Add progress dialog for number synthesis.
+ Fix the error of dimensional synthesis.
+ Fix the bug of number synthesis when import from mechanism.
+ Image background color fixed for structural synthesis atlas.

**Development**:

+ Methods and function naming corrections of Cython libraries.
+ Removed NetworkX requirement.
+ Two functions are moved to core kernel. ("edges_view" and "graph2vpoints")
+ Add "--platform" argument for Qt plugins.
+ Optimization of joint type of "VPoint" class from core kernel.
+ Update SHELL variable of Makefile on Windows platform.
+ Environment of Visual Studio 2017 version 15.8 supported. (`_MSC_VER == 1915`)

**Features**:

+ UI improvement of structural synthesis and collection panel.
+ Record inspected information.
+ Show more attributes of the graph.
+ Add "Find by links" and "Find by contracted links" buttons.
+ Add "Link as node" option in structural collection panel, but the layout is readonly.
Auto match graph assortment that came from "mechanism" page.
+ Add independent option of contracted link assortment.
+ Fix EOF error when loading edge set data from text file.
+ Removed unnecessary layout engine option.

**Development**:

+ Replaced all most NetworkX graph type to Pyslvs graph type.
+ Removed PyDot requirement.
+ Add planar graph checking of atlas algorithm.
+ Performance improvements of atlas algorithm (Object creation and function calling).

**Features**:

+ UI adjustments of "Synthesis" tab pages.
+ Adjust options of structural synthesis.
+ Remove "time and fitness" data in file format.
+ Chart dialog only shows after the algorithm completed.
+ Fixed bug in batch function of algorithm tasks.

**Development**:

+ Improvements of "Adesign" kernel.
+ Fixed an error caused by DE strategy option.
+ High performance improvements of atlas algorithm.

**Features**:

+ Fix "Save as" error on Qt slot.
+ New YAML-based file format:
+ Suffix: `.pyslvs.yml`
+ New text-based format to support version control.

**Development**:

+ Module of important widgets are be moved to `__init__.py`.
+ Fix compiler option error caused by Python (`cygwinccompiler.py`).
+ Adjust all functions and "private" methods name with PEP 8.
+ New deploy options of Github releases.

**Features**:

+ Appearance adjustments of main canvas.
+ Add scale mechanism option.
+ Change atlas algorithm "cancel" behavior to "skip":
+ Realized partial searching in atlas algorithm.
+ User can skip and keep partial result at each searching step.
+ Add fully support for macOS platform:
+ Standalone executable file compilation.
+ Automatic switch to fusion mode to avoid border too wide.
+ CI testing.
+ Add new examples:
+ "Crank slider (Three bar)"
+ "Slider lifter"
+ Input variable:
+ Support slider joint.
+ Add filter for variable list.

**Development**:

+ Using abstract class to implement partial methods.
+ Redefine solver function of Python-Solvespace.
+ Modules are renamed to lower case.
+ Add AppVeyor CI support.