feat(macros/generate/convert/auxiliary): Merge comments in c

```c
/**
  comment one
  */
/**
  comment two
  */
/**
  comment three
  */
```
is just not as readable as:
```c
/**
  * comment one
  * comment two
  * comment three
  */
```

src/macros/generate/convert/auxiliary/c/attribute/mod.rs

@@ -25,7 +25,25 @@ use crate::parser::command_spec::Attribute;
 impl Attribute {
     pub fn to_auxiliary_c(&self) -> String {
         if let Attribute::doc(doc_comment) = self {
-            format!("/**\n {}\n*/", doc_comment)
+            format!("/**\n*{}\n*/", doc_comment)
+        } else {
+            "".to_owned()
+        }
+    }
+    /// Merge mergable attributes (for example doc comments)
+    pub fn to_auxiliary_c_merged(attributes: &[Self]) -> String {
+        let doc_comments = attributes
+            .iter()
+            .map(|attr| {
+                if let Attribute::doc(doc_comment) = attr {
+                    format!("*{}\n", doc_comment)
+                } else {
+                    attr.to_auxiliary_c()
+                }
+            })
+            .collect::<String>();
+        if !attributes.is_empty() {
+            format!("/**\n{}*/", doc_comments)
         } else {
             "".to_owned()
         }

src/macros/generate/convert/auxiliary/c/enumeration/mod.rs

@@ -24,11 +24,7 @@ use crate::parser::command_spec::{Attribute, DocIdentifier, Enumeration};
 
 impl Enumeration {
     pub fn to_auxiliary_c(&self) -> String {
-        let doc_comments: String = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
         let ident = &self.identifier.to_auxiliary_c();
         let states = self
             .states

src/macros/generate/convert/auxiliary/c/function/mod.rs

@@ -27,11 +27,7 @@ use crate::parser::command_spec::{Attribute, Function, Identifier, NamedType};
 
 impl Function {
     pub fn to_auxiliary_c(&self, namespaces: &[&Identifier]) -> String {
-        let doc_comments: String = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
         let ident = self.identifier.to_c_with_path(namespaces);
         let inputs: Vec<TokenStream2> = self.inputs.iter().map(NamedType::to_auxiliary_c).collect();
 

src/macros/generate/convert/auxiliary/c/identifier/doc_identifier.rs

@@ -24,11 +24,7 @@ use crate::parser::command_spec::{Attribute, DocIdentifier};
 
 impl DocIdentifier {
     pub fn to_auxiliary_c(&self) -> String {
-        let doc_comments: String = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
         let ident = &self.name;
         format!("{}{},", doc_comments, ident)
     }

src/macros/generate/convert/auxiliary/c/namespace/mod.rs

@@ -102,11 +102,7 @@ impl Namespace {
     }
     pub fn to_auxiliary_c_full_typedef(&self) -> String {
         let ident = format_ident!("{}", self.name.name);
-        let doc_comments = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
 
         let functions: TokenStream2 = self
             .functions

src/macros/generate/convert/auxiliary/c/structure/mod.rs

@@ -24,11 +24,7 @@ use crate::parser::command_spec::{Attribute, DocNamedType, Structure};
 
 impl Structure {
     pub fn to_auxiliary_c(&self) -> String {
-        let doc_comments: String = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
         let ident = self.identifier.to_rust();
         let contents = self
             .contents

src/macros/generate/convert/auxiliary/c/type/doc_named_type.rs

@@ -24,11 +24,7 @@ use crate::parser::command_spec::{Attribute, DocNamedType};
 
 impl DocNamedType {
     pub fn to_auxiliary_c(&self) -> String {
-        let doc_comments: String = self
-            .attributes
-            .iter()
-            .map(Attribute::to_auxiliary_c)
-            .collect::<String>();
+        let doc_comments: String = Attribute::to_auxiliary_c_merged(&self.attributes);
         let ident = &self.name.to_rust();
         let r#type = self.r#type.to_auxiliary_c(false);
         format!("{}{} {};", doc_comments, r#type, ident)