adding new package icon (dotnet#377)

* adding new package icon

* updating icon source file

Clean up README (dotnet#359)

- Fixed some content wording
- Fixed markdown lint errors & warnings
- Added table of contents

Merging assembly versioning fixes (dotnet#212)

* changed 2015 to 2017 for VS build instructions

* better version of VS build section

* .gitignore: added *.orig

* update readme for 2.7.2 tagging

Merge pull request dotnet#162 from twsouthwick/disable-symbols

Exclude symbols from signing and artifacts

Release of Open XML SDK Version 2.6.0

Clean version after fixing white space, fixing encoding, making sure …

…that every file contains a BOM

Version 2.5