Spruce-up the READMEs (#3410)

- Overhaul the README to check links, update formatting, fix lint warnings and lots of other goodness.
- Add configuration for the Visual Studio spellchecker.

Contributes to #3365.

Author: martincostello

.editorconfig

@@ -9,6 +9,10 @@ root = true
 end_of_line = CRLF
 insert_final_newline = true
 
+# Visual Studio Spell Checker
+spelling_exclusion_path = .\exclusion.dic
+spelling_languages = en-us
+
 [*.{config,cs,xml}]
 indent_style = space
 indent_size = 4
@@ -40,4 +44,4 @@ indent_size = unset
 indent_style = unset
 insert_final_newline = false
 tab_width = unset
-trim_trailing_whitespace = false
+trim_trailing_whitespace = false