Move the function mkdirp into common to be generally available.
Use the new common.mkdirp from create_user_directory() from
core/init.lua replacing previous parent directory creation code
within the function.
The previous mkdirp function did not work on Windows where
absolute paths starts with a drive letter. The code from
create_user_directory() did not have this problem but was wrong
in the way it was creating the nested directories.
The new implementation in common.mkdirp fix both problems.
If a non-existing file is specified with the command "core:open-file"
a new document is opened with the given filename provided the directory
already exists.
The flag new_file is set to true in the Doc instance.
The file will be actually created only when the "save" command is used.
The document will be marked with the "*" event when no changes are done
to mean that it is a new file and is not yet saved.
The function common.normalize_path now process the .. and . in the
filename. Before was not needed because system.absolute_path already
get rid of them but now we need to have the absolute path of files
that not yet exists so we cannot use system.absolute_path.
Use the function defined in the "common" module.
Move the check for not-nil filename from common.normalize_path
to core.open_doc. In this latter the filename can be nil if a
new unnamed document is created.