Added ESNfitted function

[MartinuzziFrancesco]

This adds a ESNfitted function following the indications discussed in #92

[codecov]

Codecov Report

Merging #93 (6f7647e) into master (9245884) will increase coverage by 2.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   81.64%   83.64%   +2.00%     
==========================================
  Files          17       16       -1     
  Lines         899     1009     +110     
==========================================
+ Hits          734      844     +110     
  Misses        165      165              

Impacted Files	Coverage Δ
src/echostatenetwork.jl	96.66% <100.00%> (+1.86%)	⬆️
src/nla.jl	100.00% <0.00%> (ø)
src/hesn.jl	100.00% <0.00%> (ø)
src/train.jl	100.00% <0.00%> (ø)
src/reca_gol.jl	100.00% <0.00%> (ø)
src/reca_discrete.jl	100.00% <0.00%> (ø)
src/leaky_fixed_rnn.jl	100.00% <0.00%> (ø)
src/esn_input_layers.jl	100.00% <0.00%> (ø)
src/gameoflife.jl	91.66% <0.00%> (+0.36%)	⬆️
... and 6 more

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