Added suport for multiline variables from sh

Instead of giving an error on multiline results from sh, the results are
now stored as is, except that the last newline is stripped away to make
the output of most commands easy to use in shell commands.

Two helper functions have been added to help deal with multi-line
results. In addition, previous PascalCase template function names have
been renamed to camelCase for consistency with the sprig lib.

testdata/vars/multiline/Taskfile.yml

@@ -0,0 +1,43 @@
+default:
+  vars:
+    MULTILINE: "\n\nfoo\n  bar\nfoobar\n\nbaz\n\n"
+  cmds:
+    - task: file
+      vars:
+        CONTENT:
+          sh: "echo 'foo\nbar'"
+        FILE: "echo_foobar.txt"
+    - task: file
+      vars:
+        CONTENT:
+          sh: "echo -n 'foo\nbar'"
+        FILE: "echo_n_foobar.txt"
+    - task: file
+      vars:
+        CONTENT:
+          sh: echo -n "{{.MULTILINE}}"
+        FILE: "echo_n_multiline.txt"
+    - task: file
+      vars:
+        CONTENT: "{{.MULTILINE}}"
+        FILE: "var_multiline.txt"
+    - task: file
+      vars:
+        CONTENT: "{{.MULTILINE | catLines}}"
+        FILE: "var_catlines.txt"
+    - task: enumfile
+      vars:
+        LINES: "{{.MULTILINE}}"
+        FILE: "var_enumfile.txt"
+file:
+  cmds:
+    - |
+      cat << EOF > '{{.FILE}}'
+      {{.CONTENT}}
+      EOF
+enumfile:
+  cmds:
+    - |
+      cat << EOF > '{{.FILE}}'
+      {{range $i, $line := .LINES| splitLines}}{{$i}}:{{$line}}
+      {{end}}EOF