Added a separate output module that is used to manage the output file.

Added a separate output module that is used to manage the output file.

Fixed the -E switch: Output was always sent to stdout and an empty assembler
output file was generated. Now the output is sent to either <inputstem>.i or
the file named in the -o option.

git-svn-id: svn://svn.cc65.org/cc65/trunk@3955 b7a2c559-68d2-44c3-8de9-860c34a00d81