add support for cross, crossover and crossunder

[tsuz]

Tested using this pinescript

code

//@version=5
indicator("go-pine Crossover Test", overlay = false)

openval  = array.from(11.3, 12.9, 11.0, 19.2, 18.1, 19.4, 19.1, 10.6, 18.8, 17.1)
highval  = array.from(19.7, 19.1, 18.8, 19.6, 19.5, 19.8, 19.5, 19.9, 19.0, 17.6)
lowval   = array.from(11.1, 12.3, 10.3, 11.7, 11.2, 13.5, 12.9, 10.3, 12.4, 10.0)
closeval = array.from(16.5, 18.7, 18.2, 11.9, 19.3, 14.2, 14.4, 11.0, 14.7, 10.3)
volumeval= array.from(11.6, 13.0, 13.8, 15.9, 16.8, 19.1, 14.7, 11.7, 17.4, 15.0)

vals (index) =>
    if index >= 0 and array.size(closeval) > index
        [array.get(openval, int(index)),array.get(highval, int(index)),array.get(lowval, int(index)),array.get(closeval, int(index)), array.get(volumeval, int(index))]


[o, h, l, c, v] = vals(array.size(openval) - (last_bar_index - bar_index))

hlc3v = (h + l + c) / 3


// the same on pine
f_bb(src, length, mult) =>
    float basis = ta.sma(src, length)
    float dev = mult * ta.stdev(src, length)
    [basis, basis + dev, basis - dev]

co = ta.crossover(c, o)
co2 = ta.crossunder(c, o)
co3 = ta.cross(c, o)
// [m1, u1, l1] = f_bb(c, 4, 2.5)

// plot(adx2-adx , color=color.white)
plot(c, color=color.blue)
plot(co3  ? 1.0:0.0, color=color.yellow)

[codecov]

Codecov Report

Merging #55 (6495b7e) into main (16f9654) will increase coverage by 0.06%.
The diff coverage is 91.89%.

❗ Current head 6495b7e differs from pull request most recent head c25aadd. Consider uploading reports for the commit c25aadd to get more accurate results

@@            Coverage Diff             @@
##             main      #55      +/-   ##
==========================================
+ Coverage   81.61%   81.68%   +0.06%     
==========================================
  Files          27       28       +1     
  Lines        1632     1654      +22     
==========================================
+ Hits         1332     1351      +19     
- Misses        219      221       +2     
- Partials       81       82       +1     

Impacted Files	Coverage Δ
pine/series_crossover.go	85.00% <85.00%> (ø)
pine/series_mfi.go	86.95% <100.00%> (+1.47%)	⬆️
pine/value_series.go	97.00% <100.00%> (-0.08%)	⬇️

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