Allow passing the delimiter to PastEvent::addArgumentArray()

Added a delimiter as an argument and changed the method doc.

Nice work :)
Some nitpicks:

1. +++ b/modules/past_db/src/Entity/PastEvent.php
   @@ -237,10 +237,10 @@ class PastEvent extends ContentEntityBase implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, $delimiter, array $data, array $options = array()) {
   
   +++ b/modules/past_simpletest/src/Entity/PastEventSimpletest.php
   @@ -102,10 +102,10 @@ class PastEventSimpletest implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, $delimiter, array $data, array $options = array()) {
   
   +++ b/src/PastEventInterface.php
   @@ -183,7 +185,7 @@ interface PastEventInterface {
   +  public function addArgumentArray($key_prefix, $delimiter, array $data, array $options = array());
   
   +++ b/src/PastEventNull.php
   @@ -23,7 +23,7 @@ class PastEventNull implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, $delimiter, array $data, array $options = array()) {
   

   I think we can also assign a default value to this delimiter, since it used ':' then this should be the default (?).
   And probably better to have it as the last param.

2. +++ b/src/PastEventInterface.php
   @@ -167,10 +167,12 @@ interface PastEventInterface {
   +   *   The delimiter of the arguments.
   

   Then the param doc should be helpful for the ones that read it, so you need to specify the default value here as well.

3. +++ b/src/PastEventInterface.php
   @@ -167,10 +167,12 @@ interface PastEventInterface {
   +   * The key for each will consist of the $key_prefix_$delimiter_$array_key
   

   Better $key_prefix . $delimiter . $array_key.
   Also missing ending sentence dot :)

And don't forget to assign the issue to yourself! ;)

Cool, coolcoolcoolcool! *abed style* :)
Just some code style things xd

1. +++ b/modules/past_db/src/Entity/PastEvent.php
   @@ -237,7 +237,7 @@ class PastEvent extends ContentEntityBase implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, array $data, array $options = array(), $delimiter = ':') {
   
   +++ b/modules/past_simpletest/src/Entity/PastEventSimpletest.php
   @@ -102,7 +102,7 @@ class PastEventSimpletest implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, array $data, array $options = array(), $delimiter = ':') {
   
   +++ b/src/PastEventInterface.php
   @@ -167,25 +167,25 @@ interface PastEventInterface {
   +  public function addArgumentArray($key_prefix, array $data, array $options = array(), $delimiter = ':');
   
   +++ b/src/PastEventNull.php
   @@ -23,7 +23,7 @@ class PastEventNull implements PastEventInterface {
   +  public function addArgumentArray($key_prefix, array $data, array $options = array(), $delimiter = ':') {
   

   Since we are touching these lines, we can also do that small code style thingy about the array syntax :D

2. +++ b/src/PastEventInterface.php
   @@ -167,25 +167,25 @@ interface PastEventInterface {
   +   * The key for each will consist of the $key_prefix . $delimiter . $array_key.
   

   argh, 81 chars xd

   Maybe better something like "The key for each will consists of '$key_prefix . $delimiter . $array_key'."

3. +++ b/src/PastEventInterface.php
   @@ -167,25 +167,25 @@ interface PastEventInterface {
   +   *   ':' as provided.
       * @return array
   

   Needs a white line between @params and @return :)

Fixed the code style and changed array() to [].

Last interdiff was empty, ignore comment #7.

+++ b/modules/past_db/src/Entity/PastEvent.php
@@ -237,10 +237,10 @@ class PastEvent extends ContentEntityBase implements PastEventInterface {
+    $arguments = [];

+++ b/modules/past_simpletest/src/Entity/PastEventSimpletest.php
@@ -102,10 +102,10 @@ class PastEventSimpletest implements PastEventInterface {
+    $arguments = [];

+++ b/src/PastEventNull.php
@@ -23,8 +23,8 @@ class PastEventNull implements PastEventInterface {
+    return [];

Actually I meant only the function line, but I guess this won't hurt that much as unrelated change (?)
I think it's fine.

I guess is ready now. Waiting for the maintainers review :)

Updating the issue title.

@tduong is sneaking in some array() conversions in again, I see.. ;)

@Berdir: it hurts so much, need to clean everything! .. xd

btw, after this comment about "allow grammar syntax", i pay more attention on it.. ^^'