Correct possessive uses of "it's"

I found a couple of cases where "it's" was being used instead of
the correct "its", and went through and corrected a bunch of other
instances I could find.

content/blog/hello-lektor/contents.lr

@@ -43,7 +43,7 @@ There the hacker's favorite projects like
 [Pelican](https://github.com/getpelican/pelican) or
 [Jekyll](https://jekyllrb.com/) which support generating websites out of static
 files that are tracked through version control and there are CMS systems like
-[Statamic](http://statamic.com/) which store all of it's data in flat files
+[Statamic](http://statamic.com/) which store all of its data in flat files
 — but as mentioned — needs PHP.
 
 None of those were what I was looking for.  Static file generators like Jekyll

content/contents.lr

@@ -117,7 +117,7 @@ text:
 
 ## Open Source
 
-Lektor at it's core is a three clause [BSD licensed
+Lektor at its core is a three clause [BSD licensed
 ](https://raw.githubusercontent.com/lektor/lektor/master/LICENSE) Open Source
 project written in Python and Node.js.
 ----

content/docs/api/db/types/flow/contents.lr

@@ -20,7 +20,7 @@ For configuration you can define which blocks are allowed by setting the
 that are allowed.  If not defined, all flow blocks become available.
 
 The text format for flow blocks in the `contents.lr` file looks a bit more
-complex because of it's nested nature, but in essence it's this:
+complex because of its nested nature, but in essence it's this:
 
 ```
 #### name-of-flow-block ####

content/docs/api/project/contents.lr

@@ -9,7 +9,7 @@ summary: Provides access to a project file.
 body:
 
 The project class is one of the most basic classes that Lektor uses to
-implement it's building process.  It's generated very early on when the
+implement its building process.  It's generated very early on when the
 application needs to interact with the project file on disk.  This
 class is mostly useful for building scripts that use the Lektor API and
 not so much in other situations as it's not directly playing a role in

content/docs/content/flow/contents.lr

@@ -7,7 +7,7 @@ body:
 Flow is a system in Lektor that allows you to have higher flexibility when
 creating pages.  The [Flow Type :ref](../../api/db/types/flow/) field type
 that allows you to store multiple different formats of data within the same
-field each with it's own template.
+field each with its own template.
 
 This allows you to build complex pages made from individual components.
 

content/docs/content/urls/contents.lr

@@ -15,7 +15,7 @@ URL which can be customized.  They are roughly speaking something like a
 file name.  For instance `foo-bar` can be a slug in `/foo-bar/`.  The default
 slug of a page is the ID of the page.  So if you have a page called
 `/foo/bar/contents.lr` then the default slug is `bar`.  As you can see the
-full URL is comprised of it's own slug concatenated with all the slugs of
+full URL is comprised of its own slug concatenated with all the slugs of
 all parents.
 
 Can a slug contain slashes?  Yes indeed it can.  A slug is free to contain

content/docs/guides/disqus/contents.lr

@@ -5,7 +5,7 @@ summary: Enabling disqus comments in one minute.
 body:
 
 The `disqus-comments` plugin adds support for Disqus comments to Lektor and
-with it's help you can have comments on your pages in no time.  Once the plugin
+with its help you can have comments on your pages in no time.  Once the plugin
 is enabled a `render_disqus_comments` function is available for templates which
 can render a disqus comment box.  All you need to do for this is to create your
 own Disqus community at [Disqus Engage :ext](https://publishers.disqus.com/engage).

content/docs/models/contents.lr

@@ -86,7 +86,7 @@ Models have the following options that can customize the model itself:
 - `hidden`: a boolean value that indicates if the model should be hidden from
   the UI or not.  If set to `yes` then new pages cannot select this model.
   This is very useful for models that are implied through configuration.
-- `protected`: if a model is set to protected then all of it's instances
+- `protected`: if a model is set to protected then all of its instances
   cannot be deleted once created.
 - `inherits`: if you want to inherit all fields from another model then this
   can be set to the name of another model.