Fix EOLs and Repo Settings

[tajmone]

Fix EOLs

This commit fixes some text files being indexed with CRLF or mixed EOLs, which might create problems on non-Windows OSs.

• Add .gitattributes with optimal EOL normalization settings for Nim projects (from: tajmone/nim-repository-template) and cover all file extensions used in this repository.
• Enforce the new EOL normalization rules via git add --renormalize, thus fixing those files that were indexed with CRLF or mixed EOLs.

EditorConfig

Add .editorconfig settings to enforce consistent code styles across various editors and IDEs. Most modern editors should pickup those settings from the repository, either natively or via a plugin.

Fix files that didn't pass EditoConfig validation via the EClint tool:

• Fix indentations (in a few places).
• Remove trailing whitespace (many occurrences).
• Insert newline at file end.

NOTE — The .editorconfig file could also be used to validate commits and pull requests via Travis CI using EClint by adding a .travis.yml file:

dist: trusty
git:
  depth: false
install:
  - npm install -g eclint
script:
  - eclint check

Improve Git Exclusion Patterns

Reorganize .gitignore and add new exclusions patterns for better cross-platform coverage, including some OS-specific autogenerated system files.