Dev docs: change "op code" to "opcode"

Closes #1068

_data/glossary/en/op-code.yaml

@@ -4,7 +4,7 @@
 
 required:
                                            #-------------40 characters-------------#
-    title_max_40_characters_no_formatting: Op Code
+    title_max_40_characters_no_formatting: Opcode
 
     summary_max_255_characters_no_formatting: >
         Operation codes from the Bitcoin Script language which push data
@@ -28,7 +28,7 @@ optional:
     not_to_be_confused_with_capitalize_first_letter:
 
     links_html_or_markdown_style_capitalize_first_letter:
-        - "[Op codes](/en/developer-reference#op-codes) --- Bitcoin.org Developer Reference"
+        - "[Opcodes](/en/developer-reference#opcodes) --- Bitcoin.org Developer Reference"
         - "[List of opcodes](https://en.bitcoin.it/wiki/Script) --- Bitcoin Wiki"
 
 ---

_includes/devdoc/guide_transactions.md

@@ -481,8 +481,8 @@ conditions:
   currently non-standard.
 
 * The transaction's signature script must only push data to the script
-  evaluation stack. It cannot push new OP codes, with the exception of
+  evaluation stack. It cannot push new opcodes, with the exception of
-  OP codes which solely push data to the stack.
+  opcodes which solely push data to the stack.
 
 * The transaction must not include any outputs which receive fewer than
   1/3 as many satoshis as it would take to spend it in a typical input.

_includes/devdoc/ref_transactions.md

@@ -9,7 +9,7 @@ http://opensource.org/licenses/MIT.
 
 The following subsections briefly document core transaction details.
 
-#### OP Codes
+#### OpCodes
 {% include helpers/subhead-links.md %}
 
 {% autocrossref %}
@@ -67,15 +67,15 @@ The op codes used in the pubkey scripts of standard transactions are:
 
 * [`OP_RETURN`][op_return]{:#term-op-return}{:.term} terminates the script in failure when executed.
 
-A complete list of OP codes can be found on the Bitcoin Wiki [Script
+A complete list of opcodes can be found on the Bitcoin Wiki [Script
 Page][wiki script], with an authoritative list in the `opcodetype` enum
 of the Bitcoin Core [script header file][core script.h]
 
 ![Warning icon](/img/icons/icon_warning.svg)
 **<span id="signature_script_modification_warning">Signature script modification warning</span>:**
 Signature scripts are not signed, so anyone can modify them. This
-means signature scripts should only contain data and data-pushing op
+means signature scripts should only contain data and data-pushing opcodes
-codes which can't be modified without causing the pubkey script to fail.
+which can't be modified without causing the pubkey script to fail.
 Placing non-data-pushing opcodes in the signature script currently
 makes a transaction non-standard, and future consensus rules may forbid
 such transactions altogether. (Non-data-pushing opcodes are already