fix(bg-flamegraph): ignore comment lines

This fix ignores any lines starting with a hash character in folded
stack file formats. This allows the raw output generated by Austin
3 to be imported directly without any of the extra metadata lines
littering the flame graph visualisation.

sample/profiles/stackcollapse/simple-with-invalids.txt

@@ -6,3 +6,5 @@ a;b;d 4
 a;b;c 3
 a;b 5
 invalid line
+
+# duration: 1000

src/import/bg-flamegraph.ts

@@ -1,6 +1,6 @@
 // https://github.com/brendangregg/FlameGraph#2-fold-stacks
 
-import {Profile, FrameInfo, StackListProfileBuilder} from '../lib/profile'
+import { Profile, FrameInfo, StackListProfileBuilder } from '../lib/profile'
 
 interface BGSample {
   stack: FrameInfo[]
@@ -9,9 +9,9 @@ interface BGSample {
 
 function parseBGFoldedStacks(contents: string): BGSample[] {
   const samples: BGSample[] = []
-  contents.replace(/^(.*) (\d+)$/gm, (match: string, stack: string, n: string) => {
+  contents.replace(/(^[^#\n].*) (\d+)$/gm, (match: string, stack: string, n: string) => {
     samples.push({
-      stack: stack.split(';').map(name => ({key: name, name: name})),
+      stack: stack.split(';').map(name => ({ key: name, name: name })),
       duration: parseInt(n, 10),
     })
     return match