Document the aeso_compiler module

The module doc format is loosely based on the standard erlang doc
formats.

.gitignore

@@ -16,3 +16,5 @@ _build
 .idea
 *.iml
 rebar3.crashdump
+*.erl~
+*.aes~

README.md

@@ -8,3 +8,88 @@ It is an OTP application written in Erlang and is by default included in
 [the æternity node](https://github.com/aeternity/epoch). However, it can
 also be included in other system to compile contracts coded in sophia which
 can then be loaded into the æternity system.
+
+## Modules
+
+### aeso_compiler
+
+The Sophia compiler
+
+### Description
+
+This module provides the interface to the standard Sophia compiler. It
+returns the compiled module in a map which can then be loaded.
+
+### Types
+```erlang
+contract_string() = string() | binary()
+contract_map() = #{bytecode => binary(),
+                   compiler_version => string(),
+                   contract_souce => string(),
+                   type_info => type_info()}
+type_info()
+errorstring() = binary()
+```
+### Exports
+
+#### file(File)
+#### file(File, Options) -> CompRet
+#### from_string(ContractString, Options) -> CompRet
+
+Types
+
+``` erlang
+ContractString = contract_string()
+Options = [Option]
+CompRet = {ok,ContractMap} | {error,ErrorString}
+ContractMap = contract_map()
+ErrorString = errorstring()
+```
+
+Compile a contract defined in a file or in a string.
+
+The **pp_** options all print to standard output the following:
+
+`pp_sophia_code` - print the input Sophia code.
+
+`pp_ast` - print the AST of the code
+
+`pp_types` - print information about the types
+
+`pp_typed_ast` - print the AST with type information at each node
+
+`pp_icode` - print the internal code structure
+
+`pp_assembler` - print the generated assembler code
+
+`pp_bytecode` - print the bytecode instructions
+
+#### check_call(ContractString, Options) -> CheckRet
+
+Types
+```
+ContractString = string() | binary()
+CheckRet = {ok,string(),{Types,Type | any()},Terms} | {error,Term}
+Types = [Type]
+Type = term()
+```
+Check a call in contract through the `__call` function.
+
+#### sophia_type_to_typerep(String) -> TypeRep
+
+Types
+``` erlang
+ {ok,TypeRep} | {error, badtype}
+```
+
+Get the type representation of a type declaration.
+
+#### version() -> Version
+
+Types
+
+``` erlang
+Version = integer()
+```
+
+Get the current version of the Sophia compiler.