Replaces @multi with @replicas

As requested by @gtribello (see #221)

regtest/basic/rt-multi-1/plumed.dat

@@ -3,18 +3,18 @@ p1: POSITION ATOM=1
 p2: POSITION ATOM=2
 
 # different coefficients in different replicas
-f: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS=@multi:{{1,2,3} {0,0,0} {2,4,6}} PERIODIC=NO
+f: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS=@replicas:{{1,2,3} {0,0,0} {2,4,6}} PERIODIC=NO
 
 PRINT ARG=f FILE=colvar
 
 # equivalent syntax:
-#g: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS=@multi:{{1,2,3} {1,0,3} {1,4,3}} PERIODIC=NO
-g: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS={1 @multi:{2 0 4} 3} PERIODIC=NO
+#g: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS=@replicas:{{1,2,3} {1,0,3} {1,4,3}} PERIODIC=NO
+g: COMBINE ARG=d,p1.x,p2.y COEFFICIENTS={1 @replicas:{2 0 4} 3} PERIODIC=NO
 PRINT ARG=g FILE=colvarg
 
 # different arguments in different replicas
-PRINT ARG=@multi:{d,p1.x,p2.x} FILE=multi
+PRINT ARG=@replicas:{d,p1.x,p2.x} FILE=multi
 
 # typical umbrella sampling stuff
-RESTRAINT ARG=d AT=@multi:{1,2,3} KAPPA=100
+RESTRAINT ARG=d AT=@replicas:{1,2,3} KAPPA=100
 

src/tools/Tools.cpp

@@ -220,7 +220,7 @@ bool Tools::getKey(vector<string>& line,const string & key,string & s,int rep){
       string tmp=(*p).substr(key.length(),(*p).length());
       line.erase(p);
       s=tmp;
-      const std::string multi("@multi:");
+      const std::string multi("@replicas:");
       if(rep>=0 && startWith(s,multi)){
         s=s.substr(multi.length(),s.length());
         std::vector<std::string> words=getWords(s,"\t\n ,");

src/tools/Tools.h

@@ -155,7 +155,7 @@ bool Tools::parseVector(std::vector<std::string>&line,const std::string&key,std:
   for(unsigned i=0;i<words.size();++i){
     T v;
     std::string s=words[i];
-    const std::string multi("@multi:");
+    const std::string multi("@replicas:");
     if(rep>=0 && startWith(s,multi)){
       s=s.substr(multi.length(),s.length());
       std::vector<std::string> words=getWords(s,"\t\n ,");