Require template parameter for load function

Require template parameter for load function

The implicit conversion from load(float*) to both float
and SimdFloat caused multiple issues. The primary ones:
- Extra complexity in the implementation of traits, ArrayRef, SimdReference
- required compiler tests for ambiguity
- SimdReal x = f(load(m)) //confusing broadcast if f is scalar function
- x = s*load(m) //error-prone scalar multiply if s is scalar

New syntax in templated function is load<T>(m) and in non-templated function
load<SimdReal>(m). While this is slightly longer by itself, it is clearer
and doesn't require to store values in tempories (no ambigious overload errors).

Also avoids the need for the load proxies.

Change-Id: I8109e9365e956aaea428ec338b6a810444e03d77