Add FlexLine and its method for flex resolving
Add FlexLine and its method for flex resolving

Add the 'FlexLine' struct to represent a line in flex container, and the
'flex_resolve()' method for flex lengths resolving.

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