Better handling of expressions in repl

[arnodel]

The minimal repl had a hack to deal with expressions such as '1+1'
This implements a tool in runtime package to handle those more
gracefully

[codecov]

Codecov Report

Merging #80 (e680ec6) into lua5.4 (866962c) will increase coverage by 0.08%.
The diff coverage is 85.50%.

@@            Coverage Diff             @@
##           lua5.4      #80      +/-   ##
==========================================
+ Coverage   88.50%   88.58%   +0.08%     
==========================================
  Files          95       95              
  Lines       10435    10500      +65     
==========================================
+ Hits         9235     9301      +66     
+ Misses        921      920       -1     
  Partials      279      279              

Impacted Files	Coverage Δ
lib/golib/govalue.go	94.50% <76.92%> (+2.38%)	⬆️
runtime/lib.go	79.01% <86.79%> (+1.10%)	⬆️
runtime/syntaxerror.go	100.00% <100.00%> (+22.22%)	⬆️

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