Small format fix

doc/limitations.md

 # Limitations
 
 The philosophy of mruby is to be a lightweight implementation of
-the Ruby ISO standard. These two objectives are partially contradicting
-due to the reason that Ruby is a powerful language with complex
-implementation details which are difficult to implement in a lightweight
-manner.
+the Ruby ISO standard. These two objectives are partially contradicting.
+Ruby is an expressive language with complex implementation details which
+are difficult to implement in a lightweight manner. To cope with this,
+limitations to the "Ruby Compatibility" are defined.
 
 This document is collecting these limitations.
 
@@ -13,9 +13,7 @@ This document is collecting these limitations.
 This document does not contain a complete list of limitations.
 Please help to improve it by submitting your findings.
 
-## Confirmed limitations
-
-### ```Array``` passed to ```puts```
+## ```Array``` passed to ```puts```
 
 Passing an Array to ```puts``` results in different output.
 
@@ -37,7 +35,7 @@ puts [1,2,3]
 [1, 2, 3]
 ```
 
-### ```Kernel.raise``` in rescue clause
+## ```Kernel.raise``` in rescue clause
 
 ```Kernel.raise``` without arguments does not raise the current exception within
 a rescue clause.