syntax: markdown: do not colorize text between two bold words as italic

Also, do not colorize the text between two stricken-through words,
do not colorize text immediately after an indented piece of code,
but do give color to a double trailing space.

Signed-off-by: Ryan Westlund <rlwestlund@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>

syntax/markdown.nanorc

@@ -10,20 +10,23 @@ color magenta "^[ 	]*>.*"
 color brightmagenta "^(    |	)* ? ? ?(\*|\+|-|[1-9]+\.)( +|	)"
 
 # Emphasis and strong:
-color green "\*[^*]+\*|_[^_]+_"
+color green "\*[^* 	][^*]*\*|_[^_ 	][^_]*_"
 color brightgreen "\*\*[^*]+\*\*|__[^_]+__"
 
 # Strikethrough:
-color red "~~.+~~"
+color red "~~[^~]+~~"
+
+# Line breaks:
+color ,blue "  $"
 
 # URLs and links:
 color brightblue "\[[^]]+\]\([^)]+\)"
 color brightmagenta "!?\[[^]]+\]"
 
-# Code, indented code, and fenced code:
+# Code snippet, indented code, and fenced code:
 color brightcyan "`[^`]+`"
-color brightcyan start="^(    |	)+([^*+0-9> 	-]|[*+-]\S|[0-9][^.]).*" end="^$"
-color brightcyan start="```" end="```"
+color brightcyan "^(    |	)+ *([^*+0-9> 	-]|[*+-]\S|[0-9][^.]).*"
+color brightcyan start="```" end="```$"
 
 # Headings and the underlining of headings:
 color brightyellow "^#.*"