Improve convert_gradient_stops function.
Improve convert_gradient_stops function.

Implement Specification from CSS Images 3.

Improvements:

1. Stops with positions less than preceding stops are moved.
     A common pattern is blue `70%, white 0` for sharp transitions.
2. Stop runs are correct if first stop has a position.
    The list `black 0%, red, gold` now renders the same as `black, red, gold`.
    Other runs may also be corrected.
3. Absolute length are no longer capped to 100%.

sadmansk/servo,notriddle/servo,nnethercote/servo,DominoTree/servo,saneyuki/servo,larsbergstrom/servo,notriddle/servo,KiChjang/servo,splav/servo,KiChjang/servo,paulrouget/servo,thiagopnts/servo,dati91/servo,SimonSapin/servo,DominoTree/servo,mattnenterprise/servo,thiagopnts/servo,avadacatavra/servo,nnethercote/servo,SimonSapin/servo,SimonSapin/servo,rnestler/servo,mbrubeck/servo,saneyuki/servo,eddyb/servo,fiji-flo/servo,notriddle/servo,larsbergstrom/servo,saneyuki/servo,mbrubeck/servo,KiChjang/servo,cbrewster/servo,szeged/servo,mattnenterprise/servo,cbrewster/servo,larsbergstrom/servo,canaltinova/servo,splav/servo,ConnorGBrewster/servo,CJ8664/servo,anthgur/servo,splav/servo,pyfisch/servo,canaltinova/servo,anthgur/servo,peterjoel/servo,dsandeephegde/servo,splav/servo,nnethercote/servo,splav/servo,upsuper/servo,avadacatavra/servo,dsandeephegde/servo,fiji-flo/servo,dsandeephegde/servo,SimonSapin/servo,avadacatavra/servo,peterjoel/servo,nnethercote/servo,jimberlage/servo,canaltinova/servo,paulrouget/servo,avadacatavra/servo,rnestler/servo,jimberlage/servo,emilio/servo,jimberlage/servo,saneyuki/servo,SimonSapin/servo,jimberlage/servo,anthgur/servo,szeged/servo,thiagopnts/servo,anthgur/servo,anthgur/servo,upsuper/servo,jimberlage/servo,szeged/servo,emilio/servo,eddyb/servo,larsbergstrom/servo,dsandeephegde/servo,emilio/servo,jimberlage/servo,szeged/servo,mattnenterprise/servo,rnestler/servo,szeged/servo,peterjoel/servo,peterjoel/servo,avadacatavra/servo,cbrewster/servo,sadmansk/servo,pyfisch/servo,notriddle/servo,DominoTree/servo,cbrewster/servo,dati91/servo,saneyuki/servo,DominoTree/servo,emilio/servo,DominoTree/servo,cbrewster/servo,ConnorGBrewster/servo,peterjoel/servo,larsbergstrom/servo,emilio/servo,larsbergstrom/servo,larsbergstrom/servo,sadmansk/servo,jimberlage/servo,nnethercote/servo,saneyuki/servo,paulrouget/servo,dsandeephegde/servo,KiChjang/servo,mbrubeck/servo,rnestler/servo,emilio/servo,KiChjang/servo,KiChjang/servo,dsandeephegde/servo,peterjoel/servo,saneyuki/servo,pyfisch/servo,CJ8664/servo,thiagopnts/servo,pyfisch/servo,avadacatavra/servo,CJ8664/servo,dati91/servo,fiji-flo/servo,ConnorGBrewster/servo,notriddle/servo,peterjoel/servo,CJ8664/servo,notriddle/servo,larsbergstrom/servo,notriddle/servo,DominoTree/servo,rnestler/servo,pyfisch/servo,ConnorGBrewster/servo,CJ8664/servo,dati91/servo,nnethercote/servo,upsuper/servo,fiji-flo/servo,eddyb/servo,SimonSapin/servo,ConnorGBrewster/servo,SimonSapin/servo,saneyuki/servo,thiagopnts/servo,emilio/servo,pyfisch/servo,eddyb/servo,fiji-flo/servo,szeged/servo,emilio/servo,peterjoel/servo,eddyb/servo,mbrubeck/servo,KiChjang/servo,canaltinova/servo,eddyb/servo,cbrewster/servo,DominoTree/servo,ConnorGBrewster/servo,peterjoel/servo,thiagopnts/servo,sadmansk/servo,jimberlage/servo,splav/servo,dati91/servo,DominoTree/servo,emilio/servo,paulrouget/servo,sadmansk/servo,CJ8664/servo,splav/servo,mattnenterprise/servo,nnethercote/servo,pyfisch/servo,upsuper/servo,KiChjang/servo,canaltinova/servo,pyfisch/servo,canaltinova/servo,paulrouget/servo,upsuper/servo,upsuper/servo,DominoTree/servo,cbrewster/servo,paulrouget/servo,canaltinova/servo,anthgur/servo,splav/servo,splav/servo,eddyb/servo,larsbergstrom/servo,mbrubeck/servo,dsandeephegde/servo,KiChjang/servo,mattnenterprise/servo,SimonSapin/servo,fiji-flo/servo,ConnorGBrewster/servo,szeged/servo,mattnenterprise/servo,avadacatavra/servo,sadmansk/servo,sadmansk/servo,mattnenterprise/servo,szeged/servo,dati91/servo,mbrubeck/servo,anthgur/servo,jimberlage/servo,paulrouget/servo,mattnenterprise/servo,pyfisch/servo,saneyuki/servo,mbrubeck/servo,mbrubeck/servo,nnethercote/servo,paulrouget/servo,rnestler/servo,szeged/servo,paulrouget/servo,notriddle/servo,saneyuki/servo,ConnorGBrewster/servo,CJ8664/servo,canaltinova/servo,upsuper/servo,fiji-flo/servo,anthgur/servo,dati91/servo,avadacatavra/servo,KiChjang/servo,dsandeephegde/servo,upsuper/servo,paulrouget/servo,rnestler/servo,splav/servo,thiagopnts/servo,pyfisch/servo,emilio/servo,sadmansk/servo,nnethercote/servo,larsbergstrom/servo,szeged/servo,DominoTree/servo,dati91/servo,nnethercote/servo,fiji-flo/servo,notriddle/servo,cbrewster/servo,eddyb/servo,CJ8664/servo,rnestler/servo,peterjoel/servo,thiagopnts/servo,notriddle/servo