Prettier Liquid: Filters

[charlespwd]

Followup to #41

We should now parse filters, their syntax and print them properly.

{% # positional args %}
{{ x | filter: arg1, arg2, arg3 }}

{% # kwargs %}
{{ x | filter: name: value, other: value }}

{% # mix %}
{{ x | filter: arg1, loading: "lazy" }}

As well as define how we handle long lines. According to #12 and #13—if the line must break—we want the following:

• pipe first
• first argument same line (only positional)
• liquid drop variable expression same line

That means we expect the following (with printWidth: 1):

{{ product
  | filter: arg1,
    arg2,
    arg3
  | filter2:
    key1: val1,
    key2: val2
}}

{% # I think I'd prefer this one but it feels like community prefers the above %}
{{ 
  product
  | filter: arg1,
    arg2,
    arg3
  | filter2:
    key1: val1,
    key2: val2
}}