Compile errors.mli when compiler libs are not present.
Do not eval code that hangs the process.

The most common reason is the presence of `read_line()` and infinite
loops.  Several code blocks that were not OCaml were also tagged with
`tryocaml` (there may be some left, I did not track them systematically).
Fix some misuses of ```tryocaml

Partly fixes https://github.com/ocaml/ocaml.org/issues/282
"make clean" removes all compilation generated files.
Express that "md_preprocess" depends on "code_top".
Fix COMPILER_LIBS_PREPARE when compiler libs are present.
Add dynlink to compile "code_top" for OCaml ≥ 4.00.1
Make the SOLUTION detection work with or w/o paragraphs
rework 99 problems page - lists

Refactored to fit new style of running through toplevel.
This commit completes the lists section
rework 99 problems page - arithmetic

Refactored to fit new style of running through toplevel.
This commit completes the arithmetic section
rework 99 problems page - logic and codes

Refactored logic and codes section to fit
new style of running through toplevel.
add images for 99problems binary trees
rework 99 problems page - binary trees

Refactored binary trees section to fit
new style of running through toplevel