use OasisFormat: 0.4 in _oasis
add Benchmark.Tree, a tree-based system to gather benchmarks and run all, or part, of them
Simplify and clarify the path selection
Use right associative infix operators
Remove extra newline
Tree.with_int: prefix sub-trees with the integer
Improve the documentation
Do not output separator lines when not needed
Tree.run: Allow to specify a list of paths

Thus, Tree.run_main can also deal with multiple --path options
Make Tree.run more versatile

In particular, it was not not possible before to combine the command
line options of the Tree module with other ones in order to have a
complete output (say by Arg.usage).
Allow names to contain dots to specify paths
Allow filtering trees with wildcards
Update repository in _oasis and add maintainer + bug-reports URL
Make possible to group benchmarks as a filterable tree

The goal is to be able to run a subset of the benchmarks to test the
effect of some changes because running them all would take too much
time.
Bump version to 1.4