[Feat] Implement GraphAr Spark Tools 0.1

[lixueclaire]

Is your feature request related to a problem? Please describe.
GraphAr Spark tools are required as a library for generating, loading and transforming GAR files with Apache Spark easy.

Describe the solution you'd like
GraphAr Spark tools consist of the following parts:

• Reader: for reading GAR files into Spark DataFrame [Feat] Implement GraphAr Spark Reader for reading GAR format files into Spark DataFrame #29
• Writer: for writing Spark DataFrame into GAR files [Feat] Implement GraphAr Spark Writer for writing Spark DataFrame into GAR format files #28
• IndexGenerator: for helping to generate the vertex index for vertex/edge DataFrames [Feat] Implement Graph spark IndexGenerator for helping to generate the vertex index for vertex/edge DataFrame #36
• Info Classes: for constructing and accessing the meta information of GraphAr [Feat] Implement Info class for GraphAr spark tool to construct and access the meta information of graph #32

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A clear and concise description of any alternative solutions or features you've considered.

Additional context
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[lixueclaire]

solved by #45 #51 #52