Converted all nuspec and ps1 files to UTF-8

UTF-8 is the mandatory character encoding for nuspec files, otherwise all non-ASCII characters get displayed with “�” in the Gallery, e.g.: http://chocolatey.org/packages/AnkhSvn, http://chocolatey.org/packages/RobotoFonts

Therefore I converted all nuspec files in this directory to UTF-8 and added the XML declaration: `<?xml version="1.0" encoding="utf-8"?>` like specified in the [Chocolatey wiki](https://github.com/chocolatey/chocolatey/wiki/CreatePackages#character-encoding).

I used my node script [cpkg-utf8-conv](https://github.com/TomOne/cpkg-utf8-conv) to accomplish this task.

Maybe you notice that some characters of the diff view on this page look weird, but this is a problem of GitHub. The two files *AnkhSvn.nuspec* and *RobotoFonts.nuspec* were saved in the legacy Windows-1252 encoding (often incorrectly called ANSI). In this pull request I converted them to UTF-8, but the diff view on this GitHub page still parses them as Windows-1252. But I can confirm that in the repository these files are fine. Just click on the “View file @ …” button to be convinced.

I converted the PowerShell script files to UTF-8 too.
It is not recommended to leave PowerShell scripts in the default Windows Codepage (Windos-1252 in our case). That’s very bad for i18n. If for example such a script would be executed on a Windows PC where another Windows Codepage is the default encoding, e.g. Windows-1251 for Russian, some characters would be decoded incorrectly, because PowerShell assumes the wrong character encoding. That can break the entire script. So *always* use UTF-8 for PowerShell scipts to avoid that.

Unfortunately PowerShell requires a BOM to correctly recognize UTF-8, even if a BOM for UTF-8 is [neither required nor recommended by the Unicode standard](https://en.wikipedia.org/wiki/Byte_order_mark#UTF-8) and can lead to several problems. It seems that Microsoft ignores that fact. :-1: