Revamp D2 Windows installer

- Don't download D2 files, instead embed them in the installer. Embedded folder is specified by the EmbedD2Dir define which can be specified by using /DEmbedD2Dir=<dir> to makensis.exe.
- Remove D1 and DMC logic from D2 installer. They can still be downloaded and installed by the installer but they now use their own installers like Visual D. New installer scripts for D1 and DMC are included.
- Curl support will be included by default (will require update to create_dmd_release.d).
- Improve usage instructions.
- Significant overall clean up.
Use EmbedD2Dir with release builder
Merge pull request #97 from eco/specify-installed-dir

Revamp Windows installer