release version 0.8.0

release version 0.7.7

update doc/recent_changes.md mentioning new shell command substitutio…

…n syntax `$[ ]`

bump version number to 0.7.5

reason: Scheme code now requires foreign-procedure "c_file_rename" to be registered by C code

bump version number to 0.7.4

rename (directory-list) -> (directory-list*) because Chez Scheme alre…

…ady defines (directory-list)

with slightly different API