Fix or disable conversion warnings?

[theuni]

By default, Xcode adds warnings for implicit conversions that lose precision like:
Implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'uint32_t' (aka 'unsigned int')

Noticed when testing the XCode output of #75. There are 10 instances of this and it's pretty annoying in the build logs.

For example:

size_t ComputeCapacity(uint32_t bits, size_t max_elements, uint32_t fpbits) {
    if (bits == 0) return 0;
    uint64_t base_fpbits = BaseFPBits(bits, max_elements);

Is there any interest in cleaning these up? Or would it be preferred to disable them with -Wconversion ?

[sipa]

I'm ok with adding explicit conversions to avoid these.

[theuni]

Quick naive fixes here. Want me to clean them up and PR?