Config segments with customizable variable instead of toggles

To simplify the configuration of left and right aligned segments a new customizable variable named simple-modeline-segments has been created.

Previously the visibility of the segments was managed with a function and a variable which where created with the macro used to generate segments.

Now segments are just functions and their position in the modeline is configured via the new customizable variable.

Add input method

• Add input method segment

Initial release

Several predefined segments:

• Modified/readonly indicator
• Buffer name
• Position and region info
• Version control status
• Encoding
• EOL
• Minor modes list
• Process info
• Input method
• Major mode