throw in more \0 bytes in the string specs
add spec about coroutine.yield and \0 in strings
package the spec that demonstrates gh-19
flag "yield across cback" as pending (to forget)

closes gh-19
explain LUA_LIB in readme, closes gh-12
make tiny enhancement to readme (for gh-12)
document new eval arguments, closes gh-17
stop saying `require "rufus/lua"` in the readme
add "gem version" badge
release 1.1.1
Use null-safe string method for symbols as well as strings.
Use more performant .bytesize instead of unpack('C*').size.
Add spec demonstrating failure when a symbol contains a null character.
Add more (perhaps redundant) specs to string_spec.