Finalize UPGRADING.md document

[mrook]

UPGRADING.md needs to contain all breaking changes and suggestions/steps to migrate to the new situation.

• Describe changes to filesize
• Mention dropping of support for dot notation paths and PackageAsPath task
• Describe normalization of boolean values
• Mention removal of ExportProperties
• FileHash now creates a file by default
• scpsend no longer an alias
• describe how boolean values are no longer parsed/special
• deprecated command attribute removed from ExecTask

[siad007]

We should also include a paragraph for the project attribute phingVersion and the right usage for it inside a build xml - or maybe this should be covered in the docs?! @mrook @kenguest @jawira WDYT

[jawira]

@siad007 IMHO phingVersion details should go in documentation.

[jawira]

I have added some text to UPGRADING.md, please check #1644

[jawira]

Hi, I just want to notify that I cant find PackageAsPathTask, maybe it has been removed?