Fix all RecipeMD parsing errors

It was ALWAYS "Amount must start with a number".
This refers to amounts (yield and the ingredients).

An amount sometimes break when a comma is present outside a number.
An Amount NEEDS to start with a digit
for example:
VALID
*100 g* sugar
INVALID
*circa 100 g* sugar
*??? g* sugar
*a little bit* sugar
(!) It needs to start with a digit.

All of the errors have been due to this.
The CI server exists at first error but installing RecipeMD is quite easy.

I did:
```
for file in *.md
do
  echo "$file"
  recipemd -t "$file"
done
```
which worked quite fine. It only prints the title and not the whole recipe on success and prints the error message otherwise.
Very easy.