support comma seperated option array
extract string.split()
implement meson.backend()
remove debug messages
typecheck glob args
fix quotes inside multiline strings
fix strip() with a string full of stripchars
remove broken build regeneration for now
implement disabler()
fix custom target implicit dependencies

before, custom_target naiively assumed that the first element of command
was the only implicit dependency, which not only caused builds to fail
if said element was not an absolute path (ex. 'sh'), but also failed to
capture real implicit dependencies.
fix ncurses dependency
stub more build_target kwargs
alias external_program.full_path to path
fix setting default_options within meson.build

This required added an option type which remembers what type of option
it was, as well as holding the option value.
improve summary display
support is_system include directories
add link_with to link_args before joining
don't add nonexistent include dirs

this wasn't needed before, but is now since include_directories() has
been updated to also add an include for the same directory under build,
which may not exist.
don't relativize include dirs in dep args
add include_dir under build too