[SPARK-7583] [MLLIB] User guide update for RegexTokenizer
[SPARK-7583] [MLLIB] User guide update for RegexTokenizer

jira: https://issues.apache.org/jira/browse/SPARK-7583

User guide update for RegexTokenizer

Author: Yuhao Yang <hhbyyh@gmail.com>

Closes #7828 from hhbyyh/regexTokenizerDoc.

WindCanDie/spark,setjet/spark,someorz/spark,icexelloss/spark,taroplus/spark,akopich/spark,HyukjinKwon/spark,MLnick/spark,hvanhovell/spark,aosagie/spark,JerryLead/spark,ron8hu/spark,aray/spark,actuaryzhang/spark,esi-mineset/spark,ddna1021/spark,jrshust/spark,guoxiaolongzte/spark,shuangshuangwang/spark,ddna1021/spark,jlopezmalla/spark,highfei2011/spark,pronix/spark,bravo-zhang/spark,Aegeaner/spark,shubhamchopra/spark,ericvandenbergfb/spark,markhamstra/spark,byakuinss/spark,dongjoon-hyun/spark,shaneknapp/spark,mahak/spark,apache/spark,nchammas/spark,goldmedal/spark,shubhamchopra/spark,jiangxb1987/spark,bOOm-X/spark,minixalpha/spark,zhouyejoe/spark,skonto/spark,jkbradley/spark,wzhfy/spark,SHASHANKB/spark,guoxiaolongzte/spark,rikima/spark,milliman/spark,zzcclp/spark,rednaxelafx/apache-spark,mahak/spark,wangmiao1981/spark,zzcclp/spark,BryanCutler/spark,lvdongr/spark,hvanhovell/spark,szhem/spark,JerryLead/spark,apache-spark-on-k8s/spark,gengliangwang/spark,ueshin/apache-spark,LantaoJin/spark,joseph-torres/spark,shubhamchopra/spark,wzhfy/spark,yanboliang/spark,maropu/spark,icexelloss/spark,mdespriee/spark,rednaxelafx/apache-spark,highfei2011/spark,gioenn/xSpark,loneknightpy/spark,zero323/spark,kevinyu98/spark,BryanCutler/spark,mzl9039/spark,SnappyDataInc/spark,esi-mineset/spark,hhbyyh/spark,yanboliang/spark,rezasafi/spark,lxsmnv/spark,ajaysaini725/spark,patrick-nicholson/spark,michalsenkyr/spark,dongjoon-hyun/spark,byakuinss/spark,LantaoJin/spark,sahilTakiar/spark,map222/spark,lvdongr/spark,big-pegasus/spark,aray/spark,map222/spark,poffuomo/spark,ioana-delaney/spark,dongjoon-hyun/spark,WindCanDie/spark,zhouyejoe/spark,WeichenXu123/spark,alunarbeach/spark,aokolnychyi/spark,eyalfa/spark,big-pegasus/spark,highfei2011/spark,aokolnychyi/spark,janewangfb/spark,shaneknapp/spark,debugger87/spark,brad-kaiser/spark,andrewor14/spark,patrick-nicholson/spark,poffuomo/spark,icexelloss/spark,kissmetrics/spark,highfei2011/spark,techaddict/spark,liyichao/spark,cin/spark,gioenn/xSpark,mahak/spark,narahari92/spark,jlopezmalla/spark,kiszk/spark,ptkool/spark,nlalevee/spark,markhamstra/spark,aosagie/spark,minixalpha/spark,ajaysaini725/spark,cloud-fan/spark,jlopezmalla/spark,UndeadBaneGitHub/spark,aray/spark,jrshust/spark,minixalpha/spark,andrewor14/spark,nchammas/spark,ddna1021/spark,debugger87/spark,highfei2011/spark,kiszk/spark,SnappyDataInc/spark,darionyaphet/spark,HyukjinKwon/spark,apache-spark-on-k8s/spark,metamx/spark,hvanhovell/spark,brad-kaiser/spark,apache-spark-on-k8s/spark,joseph-torres/spark,srowen/spark,xflin/spark,HyukjinKwon/spark,haowu80s/spark,tengpeng/spark,zzcclp/spark,shuangshuangwang/spark,nilsgrabbert/spark,saturday-shi/spark,xflin/spark,SnappyDataInc/spark,ptkool/spark,witgo/spark,bdrillard/spark,ConeyLiu/spark,nlalevee/spark,liutang123/spark,big-pegasus/spark,Aegeaner/spark,rezasafi/spark,LantaoJin/spark,BryanCutler/spark,shubhamchopra/spark,metamx/spark,liutang123/spark,publicRoman/spark,ericvandenbergfb/spark,jkbradley/spark,SHASHANKB/spark,ueshin/apache-spark,facaiy/spark,debugger87/spark,WeichenXu123/spark,nilsgrabbert/spark,lxsmnv/spark,stanzhai/spark,ddna1021/spark,markhamstra/spark,dhruve/spark,someorz/spark,jlopezmalla/spark,ahnqirage/spark,janewangfb/spark,kimoonkim/spark,ptkool/spark,holdenk/spark,ddna1021/spark,haowu80s/spark,haowu80s/spark,rednaxelafx/apache-spark,huang1900/spark,pronix/spark,facaiy/spark,narahari92/spark,panfengfeng/spark,zuotingbing/spark,wangyum/spark,SHASHANKB/spark,pgandhi999/spark,ioana-delaney/spark,gengliangwang/spark,dongjoon-hyun/spark,UndeadBaneGitHub/spark,stanzhai/spark,xuanyuanking/spark,andrewor14/spark,minixalpha/spark,liutang123/spark,yanboliang/spark,SnappyDataInc/spark,chuckchen/spark,WindCanDie/spark,kevinyu98/spark,dhruve/spark,wangyum/spark,UndeadBaneGitHub/spark,stanzhai/spark,brad-kaiser/spark,SHASHANKB/spark,ajaysaini725/spark,jiangxb1987/spark,yanboliang/spark,hhbyyh/spark,dongjoon-hyun/spark,mdespriee/spark,debugger87/spark,milliman/spark,caneGuy/spark,mahak/spark,debugger87/spark,witgo/spark,saltstar/spark,aray/spark,ddna1021/spark,yanboliang/spark,icexelloss/spark,gioenn/xSpark,lvdongr/spark,brad-kaiser/spark,pgandhi999/spark,joseph-torres/spark,witgo/spark,dbtsai/spark,liyichao/spark,haowu80s/spark,matthewfranglen/spark,xuanyuanking/spark,gengliangwang/spark,yanboliang/spark,srowen/spark,michalsenkyr/spark,xflin/spark,spark-test/spark,HyukjinKwon/spark,huang1900/spark,dhruve/spark,pgandhi999/spark,milliman/spark,techaddict/spark,skonto/spark,skonto/spark,saturday-shi/spark,vinodkc/spark,WindCanDie/spark,janewangfb/spark,rezasafi/spark,alunarbeach/spark,holdenk/spark,tengpeng/spark,goldmedal/spark,apache/spark,tejasapatil/spark,maropu/spark,stanzhai/spark,SHASHANKB/spark,ConeyLiu/spark,maropu/spark,SnappyDataInc/spark,saturday-shi/spark,aokolnychyi/spark,sachintyagi22/spark,akopich/spark,Aegeaner/spark,adrian-ionescu/apache-spark,mike0sv/spark,kissmetrics/spark,Panos-Bletsos/spark-cost-model-optimizer,patrick-nicholson/spark,rednaxelafx/apache-spark,rekhaj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