Add non-blocking RawTextReader & TextBuffer (#416)

This echos the addition of the non-blocking binary reader and duplicates
(with modifications) the existing RawTextReader, and TextBuffer into a
non_blocking module with the intention of updating the existing blocking
version to lean on this non-blocking version.

src/result.rs

@@ -23,6 +23,12 @@ pub enum IonError {
     #[error("ran out of input while reading {label} at offset {offset}")]
     Incomplete { label: &'static str, offset: usize },
 
+    /// Indicates that the text input did not contain enough data to perform the requested read
+    /// operation. If the input source contains more data, the reader can append it to the buffer
+    /// and try again.
+    #[error("ran out of input while reading at line: {line} column: {column}")]
+    IncompleteText { line: usize, column: usize },
+
     /// Indicates that the writer encountered a problem while serializing a given piece of data.
     #[error("{description}")]
     EncodingError { description: String },
@@ -63,6 +69,10 @@ impl Clone for IonError {
                 label,
                 offset: *offset,
             },
+            IncompleteText { line, column } => IncompleteText {
+                line: *line,
+                column: *column,
+            },
             EncodingError { description } => EncodingError {
                 description: description.clone(),
             },
@@ -111,6 +121,14 @@ pub fn incomplete_data_error_raw(label: &'static str, offset: usize) -> IonError
     IonError::Incomplete { label, offset }
 }
 
+pub fn incomplete_text_error<T>(line: usize, column: usize) -> IonResult<T> {
+    Err(incomplete_text_error_raw(line, column))
+}
+
+pub fn incomplete_text_error_raw(line: usize, column: usize) -> IonError {
+    IonError::IncompleteText { line, column }
+}
+
 /// A convenience method for creating an IonResult containing an IonError::DecodingError with the
 /// provided description text.
 pub fn decoding_error<T, S: AsRef<str>>(description: S) -> IonResult<T> {

src/text/mod.rs

@@ -1,3 +1,4 @@
+pub mod non_blocking;
 mod parent_container;
 pub(crate) mod parse_result;
 pub(in crate::text) mod parsers;

src/text/non_blocking/mod.rs

@@ -0,0 +1,2 @@
+pub mod raw_text_reader;
+pub mod text_buffer;