Usability improvements

- Preserve indentation when a line starts with a delimiter
  - Useful for aligning multi-line method chains
- Renamed `margin_{left,right}` to `{left,right}_margin
  - Makes it easier to type in (`l`, `r`)
  - `margin_{left,right}` is still supported
- Margins can be specified as the number of spaces, or as an arbitrary string

doc/easy_align.txt

@@ -95,7 +95,7 @@ try these commands:
 Notice that you can't append `\zs` to your regular expression to put delimiters
 on the left. It can be done by providing additional options.
 
-- :EasyAlign * /[:;]\+/ { 'stick_to_left': 1, 'margin_left': '' }
+- :EasyAlign * /[:;]\+/ { 'stick_to_left': 1, 'left_margin': '' }
 
 Then we get:
 
@@ -104,21 +104,21 @@ Then we get:
 
 Options keys are fuzzy-matched, so you can write as follows:
 
-- :EasyAlign * /[:;]\+/ { 'stl': 1, 'ml': '' }
+- :EasyAlign * /[:;]\+/ { 'stl': 1, 'l': '' }
 
 You can even omit spaces between the arguments, so concisely (or cryptically):
 
-- :EasyAlign*/[:;]\+/{'stl':1,'ml':''}
+- :EasyAlign*/[:;]\+/{'s':1,'l':''}
 
 Available options for each alignment are as follows.
 
-| Atrribute        | Type    | Default                 |
-| ---------------- | ------- | ----------------------- |
-| margin_left      | string  | `' '`                   |
-| margin_right     | string  | `' '`                   |
-| stick_to_left    | boolean | 0                       |
-| ignore_unmatched | boolean | 1                       |
-| ignores          | array   | `['String', 'Comment']` |
+| Atrribute        | Type             | Default                 |
+| ---------------- | ---------------- | ----------------------- |
+| left_margin      | number or string | 0                       |
+| right_margin     | number or string | 0                       |
+| stick_to_left    | boolean          | 0                       |
+| ignore_unmatched | boolean          | 1                       |
+| ignores          | array            | `['String', 'Comment']` |
 
 
 Partial alignment in blockwise-visual mode
@@ -231,14 +231,14 @@ Extending alignment rules                       *g:easy_align_delimiters*
     \ '#': { 'pattern': '#\+' },
     \ ']': {
     \     'pattern':       '[\[\]]',
-    \     'margin_left':   '',
-    \     'margin_right':  '',
+    \     'left_margin':   0,
+    \     'right_margin':  0,
     \     'stick_to_left': 0
     \   },
     \ ')': {
     \     'pattern':       '[()]',
-    \     'margin_left':   '',
-    \     'margin_right':  '',
+    \     'left_margin':   0,
+    \     'right_margin':  0,
     \     'stick_to_left': 0
     \   }
     \ }