#1244 Use [].copy and path.exists instead of more cumbersome solutions

#1244 Slightly optimized create_highlighted_versions.py so that it won't walk the source path when it should be skipping the file

#1244 Updated README.md in plaintext source folder

#1244 Added extra option loading from `bat_options` file in directory and significantly reduced size of plaintext source

#1244 Updated create_highlighted_versions.py to ignore README.md files and use the --show-all option for manually-defined binary files

#1244 Updated plaintext file with command

bat -A --no-config --style=plain --color=always --theme='1337' --italic-text=always src/Plaintext/plaintext.txt > highlighted/Plaintext/plaintext.txt

#1244 Added example plaintext file

tests/syntax-tests/source/Plaintext/README.md

@@ -0,0 +1,10 @@
+This text file was generated with the following script. Certain invalid characters were removed manually:
+
+```python
+with open("plaintext.txt", "w"):
+    for i in range(0x10FFFF):
+        try:
+            f.write(chr(i) + "\n")
+        except:
+            pass
+```

tests/syntax-tests/source/Plaintext/bat_options

@@ -0,0 +1 @@
+--show-all