With Keyman Developer 7.0, you can edit text files containing Unicode characters encoded as UTF-8 and UTF-16. Keyboard source files can contain Unicode characters, as well as U+xxxx codes to represent them (U+xxxx codes are perhaps better in some circumstances).
You can convert a file between the standard ANSI encoding, UTF-8, and UTF-16 using the file format dropdown list on the toolbar. Note that any Unicode characters in the file will be lost if it is converted to ANSI.
Keyman Developer 7.0 also allows you to create and edit XML and HTML documents, with syntax highlighting to easily distinguish the different parts of the files. This is intended primarily for editing HTML Readme files for keyboards, but is not limited to that. Note that XML and HTML documents can also be saved as UTF-8 or UTF-16.