sv: add a few more functions

* alisp.org: reset state of Unit tests to TODO

* alisp.org: take sv_t tasks out of the backlog and set to WIP

* sv: add prototypes for sv_chop_{left,right} and sv_substr

* sv: implement sv_chop_{left, right} and sv_substr

* sv: sv_till and sv_while

* sv: add sv_truncate

When you just want to decrease to a specific size, sv_chop_right is a
bit cumbersome.

* alisp.org: Update and adjust

include/alisp/sv.h

@@ -26,6 +26,13 @@ typedef struct
 
 // String view functions
 sv_t sv_copy(sv_t);
+sv_t sv_chop_left(sv_t, u64 size);
+sv_t sv_chop_right(sv_t, u64 size);
+sv_t sv_substr(sv_t, u64 position, u64 size);
+sv_t sv_truncate(sv_t, u64 newsize);
+
+sv_t sv_till(sv_t, const char *reject);
+sv_t sv_while(sv_t, const char *accept);
 
 #endif