Fix links in README.md (#140)

Fix broken links in README.md and rewrap some lines. Fixes #139.

Author: aheejin

README.md

@@ -2,12 +2,11 @@
 
 # Exception Handling Proposal for WebAssembly
 
-This repository
-holds a
-[proposal](https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md) for
-adding exception handling to WebAssembly.
+This repository holds a [proposal](proposals/exception-handling/Exceptions.md)
+for adding exception handling to WebAssembly.
 
-* See the [proposal overview](proposals/Exceptions.md) for a summary of the proposal.
+* See the [proposal overview](proposals/exception-handling/Exceptions.md) for a
+summary of the proposal.
 
 The repository is now based on the [reference types proposal](proposals/reference-types/Overview.md) and includes all respective changes.
 
@@ -23,14 +22,15 @@ specification language.
 It also holds the WebAssembly testsuite, which tests numerous aspects of
 conformance to the spec.
 
-View the work-in-progress spec at [webassembly.github.io/spec](https://webassembly.github.io/spec/).
+View the work-in-progress spec at
+[webassembly.github.io/spec](https://webassembly.github.io/spec/).
 
 At this time, the contents of this repository are under development and known
 to be "incomplet and inkorrect".
 
 Participation is welcome. Discussions about new features, significant semantic
 changes, or any specification change likely to generate substantial discussion
-should take place in
-[the WebAssembly design repository](https://github.com/WebAssembly/design)
-first, so that this spec repository can remain focused. And please follow the
-[guidelines for contributing](Contributing.md).
+should take place in [the WebAssembly design
+repository](https://github.com/WebAssembly/design) first, so that this spec
+repository can remain focused. And please follow the [guidelines for
+contributing](Contributing.md).