Spelling corrections for src directory

Spelling corrections as found by codespell and in #561.

Some reported problems were already fixed, others are fixed here, with some exceptions (a,o.):
- "referenceby" in defgen.cpp as this is in the output and I cannot oversee the consequences (looks like none, but ...)
- "HANGEUL_CHARSET" left as is as in some MS documentation is written: 'HANGUL_CHARSET: Also spelled "Hangeul". Specifies the Hangul Korean character set.' (https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-wmf/0d0b32ac-a836-4bd2-a112-b6000a1b4fc9).

1 files changed, 1 insertions, 1 deletions

diff --git a/src/htmlhelp.cpp b/src/htmlhelp.cpp
index 20cb6ca..c514102 100644
--- a/src/htmlhelp.cpp
+++ b/src/htmlhelp.cpp
@@ -93,7 +93,7 @@ HtmlHelpIndex::~HtmlHelpIndex()
 }
 
 /*! Stores an item in the index if it is not already present. 
- *  Items are stored in alphetical order, by sorting on the
+ *  Items are stored in alphabetical order, by sorting on the
  *  concatenation of \a level1 and \a level2 (if present).
  *
  *  \param level1 the string at level 1 in the index.