Builder: Summary of segment qualifiers

`SegName DISCARD`	The segment name is allowed in the .spt file but will not output anything
`SegName ONEONLY`	The source lines are emitted only from the first .spt file processed, and are positioned according to the position of the segment in the build file
`SegName ONCEINLINE`	The source lines are emitted only from the first .spt file processed, and are positioned according to their position in the source (.spt) file

`;<SegName>`	Code down to the next segment is emitted subject to any qualifiers in the build file. Error if the segment name is not listed in the build file.
`;<=IF SegName>`	The rest of this line is emitted, in the same position as in the source file, only if the segment name is listed in the build file without a DISCARD qualifier. No error (or warning!) if not in the build file.