Change the default arithmetic of * for Normed to wrapping

[kimikage]

The implementation of multiplication for Normed was changed in PR #213, but its arithmetic defaulted to checked arithmetic for backward compatibility.

Although the discussion in Discourse is not aimed solely at building specific consensus, but at least, there is no objection to changing the default arithmetic of multiplication for Normed to wrapping arithmetic (i.e. Option 2.).

So this PR changes the default arithmetic to wrapping. This increases the risk of not noticing the overflow, but improves the consistency of the arithmetic rules.

julia> 1N0f8 * 1N0f8 # N0f8, N0f16, N0f32 and N0f64 are not affected by this change because they do not cause overflow
1.0N0f8

julia> 3N4f12 * 7N4f12 # v0.8
ERROR: ArgumentError: Normed{UInt16,12} is a 16-bit type representing 65536 values from 0.0 to 16.0037; cannot represent 21.0

julia> 3N4f12 * 7N4f12 # w/o this PR
ERROR: OverflowError: 3.0N4f12 * 7.0N4f12 overflowed for type N4f12

julia> 3N4f12 * 7N4f12 # with this PR
4.9961N4f12

You can still use checked arithmetic explicitly.

julia> using Base.Checked

julia> checked_mul(3N4f12, 7N4f12)
ERROR: OverflowError: 3.0N4f12 * 7.0N4f12 overflowed for type N4f12

[codecov]

Codecov Report

Merging #236 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
- Coverage   96.47%   96.46%   -0.01%     
==========================================
  Files           6        6              
  Lines         737      736       -1     
==========================================
- Hits          711      710       -1     
  Misses         26       26              

Impacted Files	Coverage Δ
src/normed.jl	95.90% <ø> (-0.02%)	⬇️

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[kimikage]

I will do a final confirmation before releasing v0.9.