Update headings in memap.md

Change title for brevity and heading sizes for proper rendering.

Author: Amanda Butler

docs/reference/runtime/memap.md

@@ -1,10 +1,10 @@
-<h3 id="memap">memap - static memory map analysis</h3>
+<h2 id="memap">Static memory map analysis</h2>
 
 **memap** is a simple utility that displays static memory information required by [Arm Mbed](https://github.com/mbedmicro/mbed) applications. This information is produced by analyzing the memory map file previously generated by your toolchain.
 
 <span class="notes">**Note:** This tool shows static RAM usage and the total size of allocated heap and stack space defined at compile time, not the actual heap and stack usage (which may be different depending on your application).</span>
 
-#### Using memap
+### Using memap
 
 memap is automatically invoked after an Mbed build finishes successfully. It's also possible to manually run the program with different command-line options, for example:
 
@@ -55,7 +55,7 @@ Total Flash memory (text + data + misc): 66014 bytes
 
 ```
 
-#### Information on memory sections
+### Information on memory sections
 
 The table above showed multiple memory sections.
 
@@ -70,11 +70,11 @@ There are other entries that require a bit of clarification:
 - `Fill`: represents the bytes in multiple sections (RAM and Flash) that the toolchain has filled with zeros because it requires subsequent data or code to be aligned appropriately in memory.
 - `Misc`: usually represents helper libraries introduced by the toolchain (like ``libc``), but can also represent modules that are not part of Mbed.
 
-#### Current support
+### Current support
 
 We have tested memap on Windows 7, Linux and Mac OS X. The `GCC_ARM` (GNU Arm Embedded Toolchain), Arm Compiler 5, Arm Compiler 6 and IAR toolchains generate memory map files.
 
-#### Known issues and new features
+### Known issues and new features
 
 This utility is considered "alpha" quality at the moment. The information generated by this utility may not be fully accurate and may vary from one toolchain to another.