feat: Migrate to .NET Core 3.1 (#2)

# Summary
This feature migrates the project to .NET Core (3.1).
It also introduces C#8 Nullable reference types language feature in SuperMassive core project.
Other improvements are some code clean up, minor refactoring and test coverage.

It is a preparatory work before a complete API overhaul, forecasting version 3.0.

# Changes

* feat: migrate projects to .NET Core 3.1
* feat(core): introduce nullable reference types on SuperMassive core library
* refactor(core): various clean up
* refactor(*): change directory structure
* chore(*): migrate projects to .NET Core 3.1
* chore(build): delete useless scripts
* chore(build): add github workflow for continuous integration
* test(core): add some coverage
* doc: update readme

.editorconfig

@@ -1,13 +1,38 @@
+# editorconfig.org
+
+# Default settings:
+# A newline ending every file
+# Use 4 spaces as indentation
 [*]
-end_of_line = crlf
+insert_final_newline = true
 indent_style = space
 indent_size = 4
-charset = utf-8
 trim_trailing_whitespace = true
-insert_final_newline = true
+charset = utf-8
+end_of_line = lf
+
+[*.json]
+indent_size = 2
 
-[*.xml]
+[*.{ps1,psm}]
 indent_size = 2
 
-[*.csproj]
+# Xml project files
+[*.{csproj,vcxproj,vcxproj.filters,proj,nativeproj,locproj}]
 indent_size = 2
+
+# Xml build files
+[*.builds]
+indent_size = 2
+
+# Xml files
+[*.{xml,stylecop,resx,ruleset}]
+indent_size = 2
+
+# Xml config files
+[*.{props,targets,config,nuspec}]
+indent_size = 2
+
+# Markdown files
+[*.md]
+trim_trailing_whitespace =  false

.github/workflows/continuous.yml

@@ -0,0 +1,25 @@
+name: Continuous Integration
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Setup .NET Core
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 3.1.201
+    - name: Install dependencies
+      run: dotnet restore
+    - name: Build
+      run: dotnet build --configuration Release --no-restore
+    - name: Test & Coverage
+      run: dotnet test --no-restore --collect:"XPlat Code Coverage" --settings ./build/coverlet.runsettings -v n -r .build/