* add `@divTrunc` and `@divFloor` functions
* add `@rem` and `@mod` functions
* add compile error for `/` and `%` with signed integers
* add `.bit_count` for float primitive types
closes#217
* `@truncate` builtin allows casting to the same size integer.
It also performs two's complement casting between signed and
unsigned integers.
* The idiomatic way to convert between bytes and numbers is now
`mem.readInt` and `mem.writeInt` instead of an unsafe cast.
It works at compile time, is safer, and looks cleaner.
* Implicitly casting an array to a slice is allowed only if the
slice is const.
* Constant pointer values know if their memory is from a compile-
time constant value or a compile-time variable.
* Cast from [N]u8 to []T no longer allowed, but [N]u8 to []const T
still allowed.
* Fix inability to pass a mutable pointer to comptime variable at
compile-time to a function and have the function modify the
memory pointed to by the pointer.
* Add the `comptime T: type` parameter back to mem.eql. Prevents
accidentally creating instantiations for arrays.
remove "unnecessary if statement" error
this "depends on compile variable" code is too hard to validate,
and has false negatives. not worth it right now.
std.str removed, instead use std.mem.
std.mem.eql and std.mem.sliceEql merged and do not require explicit
type argument.
