Fix call-seq formatting (#203)

They don't work in included markdown and also need a leading `:`

<img width="791" height="442" alt="grafik"
src="https://github.com/user-attachments/assets/eca5d4c2-9597-4c58-a0cc-a4e2c9109992"
/>

Author: Earlopain

doc/strscan/methods/get_byte.md

@@ -1,6 +1,3 @@
-call-seq:
-  get_byte -> byte_as_character or nil
-
 Returns the next byte, if available:
 
 - If the [position][2]

doc/strscan/methods/get_charpos.md

@@ -1,6 +1,3 @@
-call-seq:
-  charpos -> character_position
-
 Returns the [character position][7] (initially zero),
 which may be different from the [byte position][2]
 given by method #pos:

doc/strscan/methods/get_pos.md

@@ -1,6 +1,3 @@
-call-seq:
-  pos -> byte_position
-
 Returns the integer [byte position][2],
 which may be different from the [character position][7]:
 

doc/strscan/methods/getch.md

@@ -1,6 +1,3 @@
-call-seq:
-  getch -> character or nil
-
 Returns the next (possibly multibyte) character,
 if available:
 

doc/strscan/methods/scan.md

@@ -1,6 +1,3 @@
-call-seq:
-  scan(pattern) -> substring or nil
-
 Attempts to [match][17] the given `pattern`
 at the beginning of the [target substring][3].
 

doc/strscan/methods/scan_until.md

@@ -1,6 +1,3 @@
-call-seq:
-  scan_until(pattern) -> substring or nil
-
 Attempts to [match][17] the given `pattern`
 anywhere (at any [position][2]) in the [target substring][3].
 

doc/strscan/methods/set_pos.md

@@ -1,7 +1,3 @@
-call-seq:
-  pos = n -> n
-  pointer = n -> n
-
 Sets the [byte position][2] and the [character position][11];
 returns `n`.
 

doc/strscan/methods/skip.md

@@ -1,6 +1,3 @@
-call-seq:
-  skip(pattern) match_size or nil
-
 Attempts to [match][17] the given `pattern`
 at the beginning of the [target substring][3];
 

doc/strscan/methods/skip_until.md

@@ -1,6 +1,3 @@
-call-seq:
-  skip_until(pattern) -> matched_substring_size or nil
-
 Attempts to [match][17] the given `pattern`
 anywhere (at any [position][2]) in the [target substring][3].
 

doc/strscan/methods/terminate.md

@@ -1,6 +1,3 @@
-call-seq:
-  terminate -> self
-
 Sets the scanner to end-of-string;
 returns +self+: