[filesystem] Shorten stable names and add "fs." prefixes

[class.path] -> [fs.class.path]
[path.generic] -> [fs.path.generic]
[path.cvt] -> [fs.path.cvt]
[path.fmt.cvt] -> [fs.path.fmt.cvt]
[path.type.cvt] -> [fs.path.type.cvt]
[path.req] -> [fs.path.req]
[path.member] -> [fs.path.member]
[path.construct] -> [fs.path.construct]
[path.assign] -> [fs.path.assign]
[path.append] -> [fs.path.append]
[path.concat] -> [fs.path.concat]
[path.modifiers] -> [fs.path.modifiers]
[path.native.obs] -> [fs.path.native.obs]
[path.generic.obs] -> [fs.path.generic.obs]
[path.compare] -> [fs.path.compare]
[path.decompose] -> [fs.path.decompose]
[path.query] -> [fs.path.query]
[path.gen] -> [fs.path.gen]
[path.itr] -> [fs.path.itr]
[path.non-member] -> [fs.path.nonmember]
[path.io] -> [fs.path.io]
[path.factory] -> [fs.path.factory]
[class.filesystem_error] -> [fs.class.filesystem_error]
[enum.path.format] -> [fs.enum.path.format]
[enum.file_type] -> [fs.enum.file_type]
[enum.copy_options] -> [fs.enum.copy.opts]
[enum.perms] -> [fs.enum.perms]
[enum.perm_options] -> [fs.enum.perm.opts]
[enum.directory_options] -> [fs.enum.dir.opts]
[class.file_status] -> [fs.class.file_status]
[file_status.cons] -> [fs.file_status.cons]
[file_status.obs] -> [fs.file_status.obs]
[file_status.mods] -> [fs.file_status.mods]
[class.directory_entry] -> [fs.class.directory_entry]
[directory_entry.cons] -> [fs.dir.entry.cons]
[directory_entry.mods] -> [fs.dir.entry.mods]
[directory_entry.obs] -> [fs.dir.entry.obs]
[class.directory_iterator] -> [fs.class.directory_iterator]
[directory_iterator.members] -> [fs.dir.itr.members]
[directory_iterator.nonmembers] -> [fs.dir.itr.nonmembers]
[class.rec.dir.itr] -> [fs.class.rec.dir.itr]
[rec.dir.itr.members] -> [fs.rec.dir.itr.members]
[rec.dir.itr.nonmembers] -> [fs.rec.dir.itr.nonmembers]

Author: jwakely