Re-levelization: move non-docs content, rename content→docs

For better URLs, the content folder has been renamed 'docs' and all
other files have been moved up a level. Also, non-docs images have been
moved to the static folder at the top level where they belong.

Many relative paths had to be fixed to make this work.

docs/references/http-websocket-apis/api-conventions/error-formatting.md

@@ -123,4 +123,4 @@ All methods can potentially return any of the following values for the `error` c
 - `unknownCmd` - The request does not contain a [command](../index.md) that the `rippled` server recognizes.
 - `wsTextRequired` - (WebSocket only) The request's [opcode](https://tools.ietf.org/html/rfc6455#section-5.2) is not text. <!-- SPELLING_IGNORE: opcode -->
 
-{% raw-partial file="/_snippets/common-links.md" /%}
+{% raw-partial file="/docs/_snippets/common-links.md" /%}

docs/references/http-websocket-apis/api-conventions/rate-limiting.md

@@ -64,4 +64,4 @@ The usage rate drops off exponentially over time, so a client that does not make
     - [rippled API Reference](../index.md)
         - [Error Formatting](error-formatting.md)
 
-{% raw-partial file="/_snippets/common-links.md" /%}
+{% raw-partial file="/docs/_snippets/common-links.md" /%}

docs/references/http-websocket-apis/api-conventions/request-formatting.md

@@ -137,4 +137,4 @@ The following types of changes are **non-breaking changes** and may occur withou
 - Adding a new field to a request or response, not including positional parameters.
 - Adding a new API method.
 
-{% raw-partial file="/_snippets/common-links.md" /%}
+{% raw-partial file="/docs/_snippets/common-links.md" /%}

docs/references/http-websocket-apis/api-conventions/response-formatting.md

@@ -188,7 +188,7 @@ It is generally safe to ignore this warning.
     - [The `rippled` Server](../../../concepts/networks-and-servers/index.md)
     - [Consensus](../../../concepts/consensus-protocol/index.md)
     - [Amendments](../../../concepts/networks-and-servers/amendments.md)
-        - [Known Amendments](../../../resources/known-amendments.md)
+        - [Known Amendments](/resources/known-amendments.md)
 - **Tutorials:**
     - [Get Started with XRP Ledger APIs](../../../tutorials/get-started/get-started-using-http-websocket-apis.md)
     - [Install and Update `rippled`](../../../infrastructure/installation/index.md)
@@ -196,4 +196,4 @@ It is generally safe to ignore this warning.
     - [feature method][]
     - [server_info method][]
 
-{% raw-partial file="/_snippets/common-links.md" /%}
+{% raw-partial file="/docs/_snippets/common-links.md" /%}

docs/references/http-websocket-apis/api-conventions/rippled-server-states.md

@@ -22,4 +22,4 @@ Depending on how the `rippled` server is configured, how long it has been runnin
 
 **Note:** The distinction between `full`, `validating`, and `proposing` is based on synchronization with the rest of the global network, and it is normal for a server to fluctuate between these states as a course of general operation.
 
-{% raw-partial file="/_snippets/common-links.md" /%}
+{% raw-partial file="/docs/_snippets/common-links.md" /%}