this patch is just a bunch of `sed` commands
```shell
cd compiler
sed -i 's/Pos.marked/Marked.pos/g' *.ml* **/*.ml*
sed -i 's/Pos.unmark/Marked.unmark/g' *.ml* **/*.ml*
sed -i 's/Pos\.get_position/Marked.get_mark/g' *.ml* **/*.ml*
sed -i 's/Pos\.same_pos_as/Marked.same_mark_as/g' *.ml* **/*.ml*
sed -i 's/Pos\.map_under_mark/Marked.map_under_mark/g' *.ml* **/*.ml*
sed -i 's/Pos\.mark/Marked.mark/g' *.ml* **/*.ml*
sed -i 's/Pos\.compare_marked/Marked.compare/g' *.ml* **/*.ml*
```
Adds syntactic comparison for some expressions, etc., allowing in
particular to detect syntactically equal expressions. Positions are,
obviously, ignored.
This avoids many intermediate calls to e.g. `Format.asprintf`; should result in
some cases in "more correct" use of `Format`¹, avoid the computation of unused
debug strings, and make the code more readable.
¹ for `Format` to work as expected, all intermediate calls need to go through
it. Some cases of formatting to an intermediate string then printing through Format
again are still present, but this makes the situation better.
