boot: methods (fn T.m, self by address, mutation analysis), str() of any value

Methods are functions whose first parameter is the receiver's address; a method
that changes self can't be called on a temporary or a read-only value, and
calling one on a variable keeps a parameter from being borrowed. An argument
that lives inside the receiver is copied (c.merge(c)). str(x) and print of
arrays and structs go through one formatter, as in the C++ compiler.

boot.sh: 12 passed, 0 failed, 10 skipped.

tests/run/methods_basic.out

@@ -0,0 +1,8 @@
+clicks: 7 [3, 2, 2] 7
+clicks: 7 [3, 2, 2]
+copy: 17 [3, 2, 2, 10]
+clicks: 14 [3, 2, 2, 3, 2, 2]
+a: 0 [0] | b: 8 [7, 1]
+temp: 5 []
+6
+24 23