Restrict size of input parameters

[mzaffalon]

Fix #769.

[mzaffalon]

Also fixes

using ControlSystems
A = ones(3,3);
B = ones(3,1);
C = ones(1,3);
D = 0;
lsim(ss(A,B,C,D), (x,t)->0, 0:0.1:1)

ERROR: ArgumentError: indexed assignment with a single value to possibly many locations is not supported; perhaps use broadcasting `.=` instead?
Stacktrace:

[codecov]

Codecov Report

Merging #770 (cbc7f65) into master (7029934) will increase coverage by 95.23%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master     #770       +/-   ##
===========================================
+ Coverage    0.00%   95.23%   +95.23%     
===========================================
  Files           3        4        +1     
  Lines         293      294        +1     
===========================================
+ Hits            0      280      +280     
+ Misses        293       14      -279     

Impacted Files	Coverage Δ
src/timeresp.jl	94.90% <100.00%> (+94.90%)	⬆️
src/ControlSystems.jl	100.00% <0.00%> (ø)
src/simulators.jl	87.50% <0.00%> (+87.50%)	⬆️
src/root_locus.jl	97.10% <0.00%> (+97.10%)	⬆️

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[baggepinnen]

Thanks for the PR! The two issues that are fixed by this PR should probably be added as tests?

[mzaffalon]

I pushed the tests.