fix documentation typos & style

typo corrections:
 - otherwisee --> otherwise
 - it's is --> it is
 - nuber --> number
 - will likely to use --> is likely to use
 - varaible --> variable
 - defauled --> defaulted

stylistic changes:
 - which would make --> making

doc/design.xml

@@ -68,8 +68,8 @@
       Second, imagine a reusable library which has some options and exposes
       options description in its interface. If <emphasis>all</emphasis>
       options are either ascii or Unicode, and the library does not use any
-      Unicode strings, then the author will likely to use ascii options, which
-      would make the library unusable inside Unicode
+      Unicode strings, then the author is likely to use ascii options, making
+      the library unusable inside Unicode
       applications. Essentially, it would be necessary to provide two versions
       of the library -- ascii and Unicode.
     </para>

doc/overview.xml

@@ -280,9 +280,9 @@ bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla");
                         bla bla bla
         </screen>
         The tab character is removed before output. Only one tabulator per
-        paragraph is allowed, otherwisee an exception of type
+        paragraph is allowed, otherwise an exception of type
         program_options::error is thrown. Finally, the tabulator is ignored if
-        it's is not on the first line of the paragraph or is on the last
+        it is not on the first line of the paragraph or is on the last
         possible position of the first line.
         </para>
 

include/boost/program_options/parsers.hpp

@@ -103,7 +103,7 @@ namespace boost { namespace program_options {
         and to parse the command line. It is primarily needed to
         emulate named function parameters -- a regular function with 5
         parameters will be hard to use and creating overloads with a smaller
-        nuber of parameters will be confusing.
+        number of parameters will be confusing.
 
         For the most common case, the function parse_command_line is a better
         alternative.

include/boost/program_options/variables_map.hpp

@@ -118,11 +118,11 @@ namespace boost { namespace program_options {
                 - otherwise, returns empty value
 
             - if there's defaulted value
-                - if there's next varaible map, which has a non-defauled
+                - if there's next variable map, which has a non-defaulted
                   value, return that
                 - otherwise, return value from *this
 
-            - if there's a non-defauled value, returns it.
+            - if there's a non-defaulted value, returns it.
         */
         const variable_value& operator[](const std::string& name) const;