Problem: Alloc() returning "char_u *" causes a lot of type casts.
Solution: Have it return "void *". (Mike Williams) Define ALLOC_ONE() to
check the simple allocations.
Problem: Giving error messages is not flexible.
Solution: Add semsg(). Change argument from "char_u *" to "char *", also
for msg() and get rid of most MSG macros. (Ozaki Kiichi, closes
#3302) Also make emsg() accept a "char *" argument. Get rid of
an enormous number of type casts.
Problem: Placing signs can be complicated.
Solution: Add functions for defining and placing signs. Introduce a group
name to avoid different plugins using the same signs. (Yegappan
Lakshmanan, closes#3652)
Problem: When using a job or channel value as a dict value, when turning it
into a string the quotes are missing.
Solution: Add quotes to the job and channel values. (Yasuhiro Matsumoto,
closes#1930)
Problem: Using submatch() in a lambda passed to substitute() is verbose.
Solution: Use a static list and pass it as an optional argument to the
function. Fix memory leak.
