Drop a lot of extra code from blockquotes

1st iteration before the loop is exactly the same as a part of that loop

this effectively replaces:

```
do(0)
for (i = 1; i < x; i++) do(i)
```

with:

```
for (i = 0; i < x; i++) do(i)
```

lib/rules_block/blockquote.js

@@ -34,73 +34,16 @@ module.exports = function blockquote(state, startLine, endLine, silent) {
   if (state.sCount[startLine] - state.blkIndent >= 4) { return false; }
 
   // check the block quote marker
-  if (state.src.charCodeAt(pos++) !== 0x3E/* > */) { return false; }
+  if (state.src.charCodeAt(pos) !== 0x3E/* > */) { return false; }
 
   // we know that it's going to be a valid blockquote,
   // so no point trying to find the end of it in silent mode
   if (silent) { return true; }
 
-  // set offset past spaces and ">"
-  initial = offset = state.sCount[startLine] + 1;
-
-  // skip one optional space after '>'
-  if (state.src.charCodeAt(pos) === 0x20 /* space */) {
-    // ' >   test '
-    //     ^ -- position start of line here:
-    pos++;
-    initial++;
-    offset++;
-    adjustTab = false;
-    spaceAfterMarker = true;
-  } else if (state.src.charCodeAt(pos) === 0x09 /* tab */) {
-    spaceAfterMarker = true;
-
-    if ((state.bsCount[startLine] + offset) % 4 === 3) {
-      // '  >\t  test '
-      //       ^ -- position start of line here (tab has width===1)
-      pos++;
-      initial++;
-      offset++;
-      adjustTab = false;
-    } else {
-      // ' >\t  test '
-      //    ^ -- position start of line here + shift bsCount slightly
-      //         to make extra space appear
-      adjustTab = true;
-    }
-  } else {
-    spaceAfterMarker = false;
-  }
-
-  oldBMarks = [ state.bMarks[startLine] ];
-  state.bMarks[startLine] = pos;
-
-  while (pos < max) {
-    ch = state.src.charCodeAt(pos);
-
-    if (isSpace(ch)) {
-      if (ch === 0x09) {
-        offset += 4 - (offset + state.bsCount[startLine] + (adjustTab ? 1 : 0)) % 4;
-      } else {
-        offset++;
-      }
-    } else {
-      break;
-    }
-
-    pos++;
-  }
-
-  oldBSCount = [ state.bsCount[startLine] ];
-  state.bsCount[startLine] = state.sCount[startLine] + 1 + (spaceAfterMarker ? 1 : 0);
-
-  lastLineEmpty = pos >= max;
-
-  oldSCount = [ state.sCount[startLine] ];
-  state.sCount[startLine] = offset - initial;
-
-  oldTShift = [ state.tShift[startLine] ];
-  state.tShift[startLine] = pos - state.bMarks[startLine];
+  oldBMarks  = [];
+  oldBSCount = [];
+  oldSCount  = [];
+  oldTShift  = [];
 
   terminatorRules = state.md.block.ruler.getRules('blockquote');
 
@@ -125,7 +68,7 @@ module.exports = function blockquote(state, startLine, endLine, silent) {
   //     > test
   //      - - -
   //     ```
-  for (nextLine = startLine + 1; nextLine < endLine; nextLine++) {
+  for (nextLine = startLine; nextLine < endLine; nextLine++) {
     // check if it's outdented, i.e. it's inside list item and indented
     // less than said list item:
     //
@@ -148,26 +91,24 @@ module.exports = function blockquote(state, startLine, endLine, silent) {
       // This line is inside the blockquote.
 
       // set offset past spaces and ">"
-      initial = offset = state.sCount[nextLine] + 1;
+      initial = state.sCount[nextLine] + 1;
 
       // skip one optional space after '>'
       if (state.src.charCodeAt(pos) === 0x20 /* space */) {
         // ' >   test '
         //     ^ -- position start of line here:
         pos++;
         initial++;
-        offset++;
         adjustTab = false;
         spaceAfterMarker = true;
       } else if (state.src.charCodeAt(pos) === 0x09 /* tab */) {
         spaceAfterMarker = true;
 
-        if ((state.bsCount[nextLine] + offset) % 4 === 3) {
+        if ((state.bsCount[nextLine] + initial) % 4 === 3) {
           // '  >\t  test '
           //       ^ -- position start of line here (tab has width===1)
           pos++;
           initial++;
-          offset++;
           adjustTab = false;
         } else {
           // ' >\t  test '
@@ -179,6 +120,7 @@ module.exports = function blockquote(state, startLine, endLine, silent) {
         spaceAfterMarker = false;
       }
 
+      offset = initial;
       oldBMarks.push(state.bMarks[nextLine]);
       state.bMarks[nextLine] = pos;