Conversion warnings

[EricOpitz-434]

Thanks for this beautiful library! I have integrated the library into my project and I have two comments:

1. When I activate the gcc conversion warnings (-Wconversion) I get a bunch of warnings from cc.h.
2. I'm using a map with a key of type const char *. I had to manually add this key type using CC_CMPR and CC_HASH. As I think this is a pretty common case, maybe you could consider adding this to the types that are supported out of the box.

[JacksonAllan]

Hi EricOpitz! I'm glad you're getting some use out of the library.

Regarding your points:

1. The warning levels that CC was specifically designed to support are -Wall and -Wpedantic. I considered -Wconversion during early development, but GCC was complaining a lot about the passing of signed integers into the default hash and comparison functions for corresponding unsigned integer types, and I felt that defining a separate set of default (pass-through) functions for signed integers just to silence this optional warning was unnecessary. However, this is a rather minor change that I'm willing to make. I see now that -Wconversion also causes a lot of warnings about the conversion to double when a hash table's bucket count is multiplied by its maximum allowable load factor. All those warnings can probably be silenced by adding explicit casts. So in summary, I'll try to support -Wconversion in the next update, unless there are unforeseen complications.

2. CC doesn't support const-qualified keys or elements in the general case because some containers—namely vectors, maps, and sets—move this data around internally. Obviously, this concern doesn't apply when we're talking about const-qualified pointers like const char *. Currently, string keys and elements are only supported by default via char *, so the user needs to manually cast away the const, where necessary, when inserting strings, which is hardly ideal for a library that advertises itself as "ergonomic" and is also bad from the standpoint of type safety. (Interestingly, GCC doesn't complain when the inserted key or element is a string literal.) It seems like addressing this issue will only require adding default hash and comparison functions for const char *, so again, I will do this in the next update. This issue is, by the way, the same issue flagged in Verstable, which is the basis of CC's hash-table implementation.