add foreign

build.sh

@@ -1 +1 @@
-cc -lm -lgc jk.c -o jk
+cc -lm -ldl -lgc -lffi jk.c -o jk

readme.md

@@ -271,6 +271,7 @@ r. monadic deal          yield random elt of x
 r. dyadic  roll          roll xdy (note: y is 0-based, so >xr.y for 1-based)
 e. monadic eval          eval expression, yields udf on parse error
 i. monadic import        load and eval source file
+i. dyadic  foreign       call external function (lhs is array of arguments), e.g. .5i.'libm.so:dd:sin'
 y. monadic system        exec system command (yields output)
 y. dyadic  system2       exec system command with input
 E. monadic exit          exit with exit code