[Doc] Added CONTRIBUTING.md and issue templates; updated docs

.github/ISSUE_TEMPLATE/01_bug_report.yml

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+name: Bug Report
+description: File a bug report
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before you hit the submit button:
+          * Please see our [Contribution Guidelines](https://github.com/asmjit/asmjit/blob/master/CONTRIBUTING.md).
+          * Make sure that you use a recent AsmJit (master branch) before filing a bug report.
+          * Make sure that you use logging and error handling features to collect as much information as possible, if applicable.
+  - type: textarea
+    id: issue-description
+    attributes:
+      label: Issue Description
+      description: Please share a clear and concise description of the issue and optionally provide reproducibility information and output from AsmJit's logger.
+      placeholder: Description
+    validations:
+      required: true
+  - type: dropdown
+    id: operating-system
+    attributes:
+      label: Operating System
+      multiple: true
+      options:
+        - Not specified / possibly all
+        - Windows
+        - Linux
+        - Mac
+        - Android
+        - Other
+  - type: dropdown
+    id: target-architecture
+    attributes:
+      label: Architecture
+      multiple: true
+      options:
+        - Not specified
+        - X86 / X86_64
+        - AArch32
+        - AArch64
+        - RISC-V
+        - Other

.github/ISSUE_TEMPLATE/02_feature_request.yml

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+name: Feature Request
+description: Request a new feature or enhancement
+labels: [enhancement]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before you hit the submit button:
+          * Please see our [Contribution Guidelines](https://github.com/asmjit/asmjit/blob/master/CONTRIBUTING.md).
+          * Make sure that you use a recent AsmJit (master branch) before filing a feature request.
+  - type: textarea
+    id: issue-description
+    attributes:
+      label: Issue Description
+      description: Please share a clear and concise description of a new feature or enhancement.
+      placeholder: Description
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/03_help_question.yml

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+name: Help & Questions
+description: Ask a question or get help
+labels: [question]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before you hit the submit button:
+          * Please see our [Contribution Guidelines](https://github.com/asmjit/asmjit/blob/master/CONTRIBUTING.md).
+          * [Gitter Chat](https://app.gitter.im/#/room/#asmjit:gitter.im) is usually faster to get answers.
+          * If you need a help, please include as much information as possible to make it clear what the intend is.
+  - type: textarea
+    id: issue-description
+    attributes:
+      label: Details
+      description: The description of the problem or question.
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/99_other_issues.yml

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+name: Other Issues
+description: Something that doesn't fit the other categories
+body:
+  - type: textarea
+    id: issue-description
+    attributes:
+      label: Issue Description
+      description: Please share a clear and concise description of the issue.
+      placeholder: Description
+    validations:
+      required: true