GSoC-2021 Week1: pgr_edgeColoring

[veenits123]

Changes proposed in this pull request:

• Dummy placements of all the file that is going to change during this GSoC period.

  - doc/coloring/
      - added `pgr_edgeColoring.rst`
      - updated `CMakeLists.txt`
     
  - docqueries/coloring/
      - added `doc-edgeColoring.test.sql`
      - added `doc-edgeColoring.result`
      - updated `CMakeLists.txt`
     
  - include/coloring/
      - added `pgr_edgeColoring.hpp`
      
  - include/drivers/coloring/
      - added `edgeColoring_driver.h`
      
  - pgtap/coloring/
      - edgeColoring/
          - added `edge-cases.sql`
          - added `innerQuery.sql`
          - added `no_crash_test.sql`
          - added `types_check.sql`
         
  - sql/coloring/
      - added `_edgeColoring.sql`
      - added `edgeColoring.sql`
      - updated `CMakeLists.txt`
    
  - src/coloring/
      - added `edgeColoring.c`
      - added `edgeColoring_driver.cpp`
      - updated `CMakeLists.txt`