Pyslvs-ui

**Features**:

+ Remove HDF5 format support.

**Development**:

+ Remove H5Py requirement.
+ Support PEP 517. (42)
+ Remove entry point.
+ Remove submodule.
+ Remove Makefile.

**Features**:

+ Fix joint merging function. (43)
+ Fix infinity loop of solver. (44)
+ Add pickle format. (45)
+ Enhance "Remove empty links" function. ("Remove redundant links")

**Development**:

+ None.

**Features**:

+ Fix the error caused by hanging slider joint. (41)
+ Fix slider input function. (40)

**Development**:

+ Support Python 3.9.
+ Remove psutil requirement.
+ Remove Windows testing on Travis CI.

**Features**:

+ Improve performance of meta-heuristic algorithms.
+ New solver backend.

**Development**:

+ Unify "true" and "false" to lowercase in docstring.
+ Use "isinstance" instead of "type" for checking types.
+ Test suite enhancement.
+ Parallelism synthesis.

**Known issue**:

+ Slider input is not finished yet.

**Development**:

+ This version has been skipped.

**Features**:

+ Fix the error of Yaml dumper.
+ Change the definition of Path Signature: The mapping of stroke and curvature.

**Development**:

+ Raise NotImplementedError instead of ellipse on abstract methods.