Add checked_mul for type suffix

[kimikage]

This prevents MethodError due to lexical replacement of implicit * by macros. (cf. #190 (comment))

julia> using CheckedArithmetic

julia> @checked 1N0f8
1.0N0f8

julia> julia> @checked 1N0f8 * 0.5N0f8 # binary op. `mul`s will be gradually supported.
ERROR: MethodError: no method matching checked_mul(::Normed{UInt8,8}, ::Normed{UInt8,8})

The constructors still check the input range by default.

[codecov]

Codecov Report

Merging #210 into master will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #210      +/-   ##
==========================================
+ Coverage   88.24%   88.31%   +0.07%     
==========================================
  Files           6        6              
  Lines         485      488       +3     
==========================================
+ Hits          428      431       +3     
  Misses         57       57              

Impacted Files	Coverage Δ
src/FixedPointNumbers.jl	84.52% <100.00%> (+0.28%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b7e2ae1...2a60c95. Read the comment docs.